Method and apparatus for spinal stabilization

ABSTRACT

A method and apparatus of limiting at least one degree of movement between a superior vertebral body, an inferior vertebral body, and an intermediate vertebral body that is disposed between the superior and inferior vertebral bodies of a patient. The method can comprise: advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body; positioning a proximal portion of the stabilization device such that the proximal portion limits at least one degree of movement between the superior vertebral body and the intermediate vertebral body by contacting a surface of the superior vertebral body; and advancing a distal end of a fixation device into a facet of the intermediate vertebral body and into a facet or pedicle of the inferior vertebral body for stabilizing the intermediate vertebral body and the inferior vertebral body.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/134,886, filed Jun. 6, 2008, which claims priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/942,998,filed Jun. 8, 2007, the disclosures of these applications areincorporated by reference herein in their entireties.

BACKGROUND

1. Field of the Inventions

The present inventions relate to medical devices and, more particularly,to methods and apparatuses for dynamic spinal stabilization.

2. Description of the Related Art

The human spine is a flexible weight bearing column formed from aplurality of bones called vertebrae. There are thirty three vertebrae,which can be grouped into one of five regions (cervical, thoracic,lumbar, sacral, and coccygeal). Moving down the spine, there aregenerally seven cervical vertebra, twelve thoracic vertebra, five lumbarvertebra, five sacral vertebra, and four coccygeal vertebra. Thevertebra of the cervical, thoracic, and lumbar regions of the spine aretypically separate throughout the life of an individual. In contrast,the vertebra of the sacral and coccygeal regions in an adult are fusedto form two bones, the five sacral vertebra which form the sacrum andthe four coccygeal vertebra which form the coccyx.

In general, each vertebra contains an anterior, solid segment or bodyand a posterior segment or arch. The arch is generally formed of twopedicles and two laminae, supporting seven processes—four articular, twotransverse, and one spinous. There are exceptions to these generalcharacteristics of a vertebra. For example, the first cervical vertebra(atlas vertebra) has neither a body nor spinous process. In addition,the second cervical vertebra (axis vertebra) has an odontoid process,which is a strong, prominent process, shaped like a tooth, risingperpendicularly from the upper surface of the body of the axis vertebra.Further details regarding the construction of the spine may be found insuch common references as Gray's Anatomy, Crown Publishers, Inc., 1977,pp. 33-54, which is herein incorporated by reference.

The human vertebrae and associated connective elements are subjected toa variety of diseases and conditions which cause pain and disability.Among these diseases and conditions are spondylosis, spondylolisthesis,vertebral instability, spinal stenosis and degenerated, herniated, ordegenerated and herniated intervertebral discs. Additionally, thevertebrae and associated connective elements are subject to injuries,including fractures and torn ligaments and surgical manipulations,including laminectomies.

The pain and disability related to the diseases and conditions oftenresult from the displacement of all or part of a vertebra from theremainder of the vertebral column. Over the past two decades, a varietyof methods have been developed to restore the displaced vertebra totheir normal position and to fix them within the vertebral column.Spinal fusion is one such method. In spinal fusion, one or more of thevertebra of the spine are united together (“fused”) so that motion nolonger occurs between them. The vertebra may be united with varioustypes of fixation systems. These fixation systems may include a varietyof longitudinal elements such as rods or plates that span two or morevertebrae and are affixed to the vertebrae by various fixation elementssuch as wires, staples, and screws (often inserted through the pediclesof the vertebrae). These systems may be affixed to either the posterioror the anterior side of the spine. In other applications, one or morebone screws may be inserted through adjacent vertebrae to providestabilization.

Although spinal fusion is a highly documented and proven form oftreatment in many patients, there is currently a great interest insurgical techniques that provide stabilization of the spine whileallowing for some degree of movement. In this manner, the natural motionof the spine can be preserved, especially for those patients with mildor moderate disc conditions. In certain types of these techniques,flexible materials are used as fixation rods to stabilize the spinewhile permitting a limited degree of movement.

SUMMARY

Notwithstanding the variety of efforts in the prior art described above,these techniques are associated with a variety of disadvantages. Inparticular, these techniques typically involve an open surgicalprocedure, which results higher cost, lengthy in-patient hospital staysand the pain associated with open procedures.

Therefore, there remains a need for improved techniques and systems forstabilizing the spine. For example, the devices can be implantablethrough a minimally invasive procedure.

Accordingly, one embodiment of the present inventions comprises a methodof limiting at least one degree of movement between a superior vertebralbody, an intermediate vertebral body, and an inferior vertebral body ofa patient. In accordance with an embodiment of the method, a distal endof a stabilization device can be advanced into a pedicle of theintermediate vertebral body. A proximal portion of the stabilizationdevice can be positioned such that the proximal portion limits at leastone degree of movement between a superior vertebral body and theintermediate vertebral body by contacting a surface of the superiorvertebral body. Further, the method can further comprise advancing adistal end of a fixation device into a facet of the intermediatevertebral body and into a facet of the inferior vertebral body forstabilizing the intermediate vertebral body and the inferior vertebralbody.

Some implementations of the embodiment of the method described above canbe modified such that the step of positioning a proximal portion of thestabilization device can comprise advancing a proximal anchor distallyover an elongated body of the stabilization device. Further, the step ofadvancing a proximal anchor distally over an elongated body of thestabilization device can comprise proximally retracting the elongatedbody with respect to the proximal anchor. Additionally, the step ofadvancing a proximal anchor distally over an elongated body of thestabilization device can comprise applying a distal force to theproximal anchor.

In other implementations, the method can further comprise maintainingthe patient in a face down position during the step of advancing adistal end of a stabilization device into the pedicle of theintermediate vertebral body. The step of advancing a distal end of astabilization device into a pedicle of the intermediate vertebral bodycan comprise advancing the distal end of the stabilization devicethrough the pars of the intermediate vertebral body. The steps ofadvancing a distal end of a stabilization device into a pedicle of theintermediate vertebral body and positioning a proximal portion of thestabilization device can be accomplished through a minimally invasivesurgical approach.

Further, the step of advancing a distal end of a stabilization deviceinto a pedicle of the intermediate vertebral body can comprise rotatingthe distal end of the stabilization device. Furthermore, advancing adistal end of a stabilization device into a pedicle of the intermediatevertebral body can further comprise advancing the stabilization deviceover a guidewire. In addition, advancing a distal end of a stabilizationdevice into a pedicle of the intermediate vertebral body can furthercomprise advancing the stabilization device through an expanded tissuetract.

Another embodiment comprises a method of limiting at least one degree ofmovement between a superior vertebral body and an intermediate vertebralbody of a patient. According to such an embodiment, a distal end of afirst stabilization device can be advanced into a pedicle of theintermediate vertebral body. A proximal portion of the firststabilization device can be positioned such that the proximal portionabuts against a surface of an intermediate articular process of thesuperior adjacent vertebral body to limit at least one degree ofmovement between a superior vertebral body and an intermediate vertebralbody. A distal end of a second stabilization device can be advanced intoa pedicle of the intermediate vertebral body such that it is positionedwith bilateral symmetry with respect to the first stabilization device.A proximal portion of the second stabilization device can be positionedsuch that the proximal portion abuts, with bilateral symmetry withrespect to the first stabilization device, against a surface of a secondintermediate articular process of the superior adjacent vertebral bodyto limit at least one degree of movement between the superior vertebralbody and the intermediate vertebral body. Further, the method can alsocomprise advancing a distal end of a fixation device into a facet of theintermediate vertebral body and into a facet of the inferior vertebralbody for stabilizing the intermediate vertebral body and the inferiorvertebral body.

In some implementations of the method, the first and secondstabilization devices can be used to limit extension and/or flexionbetween the superior vertebral body and the intermediate vertebral body.Further, the first and second stabilization devices can be used to limitlateral movement between the superior vertebral body and theintermediate vertebral body.

In accordance with yet another embodiment, a kit is provided for dynamicspinal stabilization. The kit can comprise one or more spinalstabilization devices and one or more orthopedic fixation devices. Eachspinal stabilization device can comprise an elongate body, a distalanchor, a retention structure, a proximal anchor, and at least onecomplementary retention structure. The elongate body can have a proximalend and a distal end. The distal anchor can be disposed on the distalend of the elongate body. The retention structure can be disposed on thebody, proximal to the distal anchor. The proximal anchor can be moveablycarried by the body, and the proximal anchor can have an outer surface,and at least a portion of the outer surface can be elastic. The at leastone complementary retention structure can be disposed on the proximalanchor and can be configured for permitting proximal movement of thebody with respect to the proximal anchor but resisting distal movementof the body with respect the proximal anchor.

The orthopedic fixation device can comprise an elongate body, a distalanchor, a retention structure, a proximal anchor, at least onecomplementary retention structure, and a washer. The elongate body canhave a proximal end and a distal end. The distal anchor can be disposedon the distal end. The retention structure can be disposed on theelongate body, proximal to the anchor. The proximal anchor can bemoveably carried by the elongate body, and the proximal anchor cancomprise a tubular sleeve and a radially outward extending head. The atleast one complementary retention structure can be disposed on theproximal anchor and can be configured for permitting proximal movementof the elongate body with respect to the proximal anchor but resistingdistal movement of the elongate body with respect the proximal anchor.The washer can be angularly moveable with respect to the longitudinalaxis of the tubular sleeve. The washer can have an aperture that iselongated with respect to a first axis such that the washer permitsgreater angular movement with respect to the longitudinal axis of thetubular sleeve in a plane containing the first axis.

In some embodiments, the kit can be configured such that the distalanchor of each stabilization device comprises a helical flange. Theretention structure on the body and the at least one complementaryretention structure on the proximal anchor of each stabilization devicecan also comprise a series of ridges and grooves. For example, the atleast one complementary retention structure on the proximal anchor ofeach stabilization device can comprise an annular ring positioned withina recess formed between the proximal anchor and the elongate pin.

Further, the proximal anchor of each stabilization device can alsoinclude a distally facing surface. The distally facing surface caninclude at least one bone engagement feature. The aperture of eachorthopedic fixation device can circumscribe a channel having a width ina first direction and a height in a second direction that isperpendicular to the first direction. The width can be smaller than themaximum diameter of the head and the height can be greater than thewidth. In addition, the distal anchor of each orthopedic fixation devicecan comprise a helical flange. In some implementations, the distalanchor of each orthopedic fixation device can be moveable from an axialorientation for distal insertion through a bore to an inclineorientation to resist axial movement through the bore.

In other embodiments, the retention structures of the elongate body andthe proximal anchor of each orthopedic fixation device can permitproximal movement of the elongate body with respect to the proximalanchor without rotation. The washer of each orthopedic fixation devicecan include a bottom wall, a side wall and a lip for retaining the headof the proximal anchor within the washer. The elongated body of eachorthopedic fixation device can comprise a first portion and a secondportion that are detachably coupled together at a junction. The firstportion of each orthopedic fixation device can include an anti-rotationstructure and the proximal anchor of each orthopedic fixation deviceincludes a complementary anti-rotation structure to prevent rotationbetween the first portion and the proximal anchor.

In yet another embodiment, a kit is provided for dynamic spinalstabilization, and can comprise one or more spinal stabilization devicesand one or more orthopedic fixation devices. The spinal stabilizationdevice can be used for limiting at least one degree of movement betweena superior vertebral body and an inferior vertebral body of a patient,and can comprise an elongate body, a distal anchor, a retentionstructure, a proximal anchor, and at least one complementary retentionstructure. The elongate body can have a proximal end and a distal end.The distal anchor can be disposed on the distal end of the elongatebody. The retention structure can be disposed on the body, proximal tothe distal anchor. The proximal anchor can be moveably carried by thebody and can include at least one flat surface configured to abutagainst a surface of an inferior articular process of the superioradjacent vertebral body when the stabilization device is inserted intothe inferior adjacent vertebral body. Finally, the at least onecomplementary retention structure can be disposed on the proximal anchorand can be configured for permitting proximal movement of the body withrespect to the proximal anchor but resisting distal movement of the bodywith respect the proximal anchor.

In such an embodiment, the orthopedic fixation device can comprise anelongate pin, at least one distal anchor, a proximal anchor, and ananti-rotational structure. The elongate pin can have a proximal end, adistal end, and a first retention structure. The at least one distalanchor can be carried by the elongate pin. The proximal anchor can beaxially moveable with respect to the elongate pin and can comprise asplit ring positioned within an annular recess formed within theproximal anchor. The split ring can have at least one gap formed betweentwo ends and can be moveable between a first position and a secondposition. The second position can be located closer to the longitudinalaxis of the elongate pin as compared to the first portion so as toengage the first retention structure and prevent proximal movement ofthe proximal anchor with respect to the elongated pin while the firstposition allows distal movement of the proximal anchor with respect tothe pin. The anti-rotational structure can prevent rotation of the splitring about the longitudinal axis of the elongate pin.

Some embodiments of the kit can be configured such that the elongate pinof each orthopedic fixation device includes at least one anti-rotationalfeature configured to engage a complementary anti-rotational feature ofthe proximal anchor. In such an embodiment, the anti-rotationalstructure of each orthopedic fixation device can position the gap of thesplit ring such that it is positioned over the anti-rotational featureof the elongate pin. Further, the anti-rotational feature of theelongate pin of each orthopedic fixation device can comprise at leastone flat side. The anti-rotational feature of each orthopedic fixationdevice can also comprise includes a pair of tabs that extend inwardlyfrom the tubular body toward the longitudinal axis of the tubular bodyand positioned between the gap of the split ring.

In additional embodiments of the kit, the distal anchor of eachorthopedic fixation device can comprise a helical flange. Further, thedistal anchor of each orthopedic fixation device can be moveable from anaxial orientation for distal insertion through a bore to an inclineorientation to resist axial movement through the bore. The elongate pinof each orthopedic fixation device can also comprise a first portion anda second portion that are detachably coupled together at a junction.Further, the first portion of each orthopedic fixation device caninclude an anti-rotation structure and the proximal anchor of eachorthopedic fixation device can include a complementary anti-rotationstructure to prevent rotation between the first portion and the proximalanchor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of the inventions disclosedherein are described below with reference to the drawings of thepreferred embodiments. The illustrated embodiments are intended toillustrate, but not to limit the inventions. The drawings contain thefollowing figures:

FIG. 1A a side elevational view of a portion of a vertebra in which astabilization device implanted therein, according to an embodiment ofthe present inventions.

FIG. 1B is a posterior view of a portion of a vertebra having twodevices similar to that of FIG. 1A implanted substantially bilaterallytherein, according to another embodiment.

FIG. 1C is a posterior view of a portion of a vertebra having twodevices similar to that of FIG. 1A implanted substantially bilaterallytherein and a member extending between the two devices, according to yetanother embodiment.

FIG. 1D is a side elevational view of a portion of a vertebrastabilization devices implanted therein, according to anotherembodiment.

FIG. 1E is a posterior view of a portion of a vertebra having fourstabilization devices similar to that of FIG. 1D implanted substantiallybilaterally therein, according to another embodiment.

FIG. 2 is a side perspective view of the stabilization device of FIGS.1A and 1B, according to an embodiment.

FIG. 3A is a side view of the stabilization device shown in FIG. 2.

FIG. 3B is a cross-sectional view of a body portion of the stabilizationdevice of FIG. 2.

FIG. 4 is a partial cross-sectional view of a proximal portion of thestabilization device shown in FIG. 2.

FIG. 5 is an enlarged view of a portion of the stabilization deviceshown in FIG. 4 taken along section 5-5.

FIG. 6 is a side perspective view of a locking ring of the stabilizationdevice shown in FIG. 3A.

FIG. 7A is a side view of a body portion of the stabilization deviceshown in FIG. 2, according to another embodiment.

FIG. 7B is an enlarged view of a portion of the stabilization deviceshown in FIG. 7A taken along section 7B-7B.

FIG. 8 is a posterior view of a portion of a vertebra having portionsthereof removed to receive a fixation device, according to anotherembodiment.

FIG. 9A is a side view of a device configured to remove portions of avertebra, according to an embodiment.

FIG. 9B is an enlarged side view of the distal end of the device shownin FIG. 9A.

FIG. 9C is a side view of a tool configured to insert a body of astabilization device, according to an embodiment.

FIG. 9D is an enlarged side view of the tool shown in FIG. 9C.

FIG. 9E is an enlarged side view of the tool shown in FIG. 9C with abody of a stabilization device inserted therein.

FIG. 10A is a side view of yet another embodiment of a stabilizationdevice.

FIG. 10B is a cross-sectional side view of the stabilization deviceshown in FIG. 10A.

FIGS. 11A and 11B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIGS. 12A and 12B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIGS. 13A and 13B are perspective rear and front views of anotherembodiment of a proximal anchor.

FIG. 14 is a side view of yet another embodiment of a proximal anchor.

FIG. 15 is a side perspective view of yet another embodiment of aproximal anchor.

FIG. 16 is a side view of yet another embodiment of a proximal anchor.

FIG. 17 is a side perspective view of an embodiment of an insertion toolconfigured to insert a proximal onto a body portion of a fixationdevice.

FIG. 18 is a cross-sectional side view of the insertion tool shown inFIG. 17.

FIG. 19 is a cross-sectional side view of a modified embodiment of astabilization device.

FIG. 20A is a side view of a modified embodiment of a stabilizationdevice in an un-expanded configuration.

FIG. 20B is a cross-sectional side view of the stabilization deviceshown in FIG. 20A in an expanded configuration.

FIG. 20C is a cross-sectional side view of the stabilization deviceshown in FIG. 20A in an un-expanded configuration.

FIG. 20D is an enlarged cross-sectional side view of the stabilizationdevice shown in FIG. 20B in an expanded configuration.

FIG. 21 is a cross-sectional side view of yet another embodiment of astabilization device in an expanded configuration.

FIG. 22 is a cross-sectional side view of yet another modifiedembodiment of a stabilization device in an expanded configuration.

FIG. 23A is a perspective view of yet another embodiment of a fixationdevice.

FIG. 23B is a side view of the fixation device shown in FIG. 23A.

FIG. 23C is a longitudinal cross-sectional view of the fixation deviceshown in FIG. 23A.

FIG. 23D is an enlarged view of a portion of the fixation device shownin FIG. 23A taken along section 23D-23D.

FIG. 24A is a perspective view of a proximal anchor, according to anembodiment.

FIG. 24B is a side view of the proximal anchor shown in FIG. 24A.

FIG. 24C is a side view of the proximal anchor shown in FIG. 24A.

FIG. 24D is a bottom view of the proximal anchor shown in FIG. 24A.

FIG. 24E is a top view of the proximal anchor shown in FIG. 24A.

FIG. 24F is a cross-sectional view of the proximal anchor shown in FIG.24A.

FIG. 25A is a perspective view of another embodiment of a proximalanchor.

FIGS. 25B and 25C are enlarged views of a portion of a proximal anchor,according to an embodiment.

FIG. 25D is a front view of the proximal anchor shown in FIG. 25A.

FIG. 26 is a posterior view of a portion of the lumbar spine with thefixation device shown in FIG. 23A being used as a trans-facet screw,according to an embodiment.

FIG. 27 is a posterior view of a portion of a vertebra having twodevices similar to that shown in FIG. 23A implanted substantiallybilaterally therein, according to an embodiment.

FIG. 28 is a side elevational view of the portion of the vertebra shownin

FIG. 27 having an exemplary embodiment of a stabilization deviceimplanted therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although embodiments of the present inventions will be disclosedprimarily in the context of a spinal stabilization procedure, themethods and structures disclosed herein are intended for application inany of a variety medical applications, as will be apparent to those ofskill in the art in view of the disclosure herein. For example, certainfeatures and aspects of bone stabilization device and techniquesdescribed herein may be applicable to proximal fractures of the femurand a wide variety of fractures and osteotomies, the hand, such asinterphalangeal and metacarpophalangeal arthrodesis, transversephalangeal and metacarpal fracture fixation, spiral phalangeal andmetacarpal fracture fixation, oblique phalangeal and metacarpal fracturefixation, intercondylar phalangeal and metacarpal fracture fixation,phalangeal and metacarpal osteotomy fixation as well as others known inthe art. See e.g., U.S. Pat. No. 6,511,481, which is hereby incorporatedby reference herein. A wide variety of phalangeal and metatarsalosteotomies and fractures of the foot may also be stabilized using thebone fixation devices described herein. These include, among others,distal metaphyseal osteotomies such as those described by Austin andReverdin-Laird, base wedge osteotomies, oblique diaphyseal, digitalarthrodesis as well as a wide variety of others that will be known tothose of skill in the art. Fractures of the fibular and tibial malleoli,pilon fractures and other fractures of the bones of the leg may befixated and stabilized with these bone fixation devices with or withoutthe use of plates, both absorbable or non-absorbing types, and withalternate embodiments of the current inventions. The stabilizationdevices may also be used to attach tissue or structure to the bone, suchas in ligament reattachment and other soft tissue attachment procedures.Plates and washers, with or without tissue spikes for soft tissueattachment, and other implants may also be attached to bone, usingeither resorbable or nonresorbable fixation devices depending upon theimplant and procedure. The stabilization devices may also be used toattach sutures to the bone, such as in any of a variety of tissuesuspension procedures. The bone stabilization device described hereinmay be used with or without plate(s) or washer(s), all of which can beeither permanent, absorbable, or combinations.

FIGS. 1A and 1B are side and rear elevational views of a dynamicstabilization device 12 positioned within a body structure 10 a of aspine. FIGS. 1D and 1E are side and rear elevational views of two pairof bone stabilization devices, such as the dynamic stabilization device12 and a fixation device 800, positioned within body structures 10 a, 10b of the spine. As will be explained in detail below, the dynamicstabilization device 12 and the fixation device 800 may be used in avariety of techniques to stabilize the spine. It should also beunderstood that the dynamic stabilization device 12 and the fixationdevice 800 may refer to more than one dynamic stabilization device 12(such as a pair of dynamic stabilization devices 12 a, 12 b) and morethan one fixation device 800 (such as a pair of fixation devices 800 a,800 b).

As discussed further herein, in some embodiments, the dynamicstabilization device(s) 12 can include an outer surface of a proximalanchor that has a smooth or spherical shape. As will be explained below,the outer surface of the proximal anchor can be configured to abutagainst the inferior facet of the superior adjacent vertebrae. In thismanner, motion between the adjacent vertebrae may be limited and/orconstrained. When combined with the fixation device(s) 800, the devices(12, 800) can be implanted to result in beneficial dynamic stabilizationof a desired portion of the spine.

In one embodiment, the dynamic stabilization device 12 can be attached(e.g., inserted or screwed into) and/or coupled to a respective bodystructures and limit motion of another respective body structure. In theanother embodiment, the dynamic stabilization device 12 can limitextension in the spine by being attached and/or coupled to a respectiveinferior body structure and limiting motion of an adjacent respectivesuperior body structure. As described herein, the superior and inferiorbody structures can refer to adjacent structures along the spine. Whendiscussing the superior body structure, it will be presumed that whenthe dynamic stabilization device 12 and the fixation device 800 shown inFIGS. 1D and 1E are both used, the devices 12 can be inserted into anintermediate body structure immediately below the superior bodystructure.

Further, the fixation device 800 can be inserted into the intermediateand the inferior body structures to secure said body structures togetherand to promote fusion between the body structures. Thus, the three bodystructures may be described as superior, intermediate, and inferior whenthe dynamic stabilization device 12 and the fixation device 800 arediscussed together, or as simply superior and inferior when the dynamicstabilization device 12 and the fixation device 800 are being discussedindividually. “Body structure” as used herein is the anterior solidsegment and the posterior segment of any vertebrae of the five regions(cervical, thoracic, lumbar, sacral, and coccygeal) of the spine. Insome embodiments, the dynamic stabilization device 12 can limit motionby contacting, abutting against and/or wedging against the adjacent bodystructure and/or a device coupled to the adjacent body structure. Thefixation device 800 can be positioned below (or above in otherembodiments) the stabilization device 12 and can be used to promotespinal fusion below the spinal level at which motion is limited by thedynamic stabilization device. In such an embodiment, the dynamicstabilization device can provide adjacent level support as an adjunct tofusion therapy. In one embodiment, the fusion therapy involves thefixation device 800, which will be described in detail below.

With reference to the illustrated embodiment of FIGS. 1A and 1B, thedistal end of the dynamic bone stabilization device 12 is inserted intothe pedicle of the inferior vertebrae, preferably through the pars(i.e., the region between the lamina and the superior articularprocesses). The proximal end of the device 12 extends above the parssuch that it limits motion of a superior adjacent vertebra 10 b withrespect to the inferior adjacent vertebrae 10 b. In one embodiment, theproximal end of the device limits motion by abutting and/or wedgingagainst a surface of the superior adjacent vertebrae as the superioradjacent vertebrae moves relative to the inferior adjacent vertebrae. Inthis manner, at least one degree of motion between the inferior andsuperior vertebrae may be limited. For example, the spine generally hassix (6) degrees of motion which include flexion, extension, left andright lateral bending and axial rotation or torsion. In the illustratedembodiment, extension of the spine is limited. Embodiments in which thedevices are inserted with bilateral symmetry can be used to limit leftand right lateral bending.

In the illustrated embodiment, motion of the spine is limited when theproximal end of the device contacts, abuts, and/or wedges against theinferior articular process of the superior adjacent vertebra 10 b. Inthis application, it should be appreciated that one or more intermediatemember(s) (e.g., plates, platforms, coatings, cement, and/or adhesives)can be can be coupled to the superior adjacent vertebra 10 b or otherportions of the spine that the device contacts, abuts, and/or wedgesagainst. Thus, in this application, when reference is made to the devicecontacting, abutting and/or wedging against a portion of the spine itshould be appreciated that this includes embodiments in which the devicecontacts, abuts and/or wedges against one or more intermediate membersthat are coupled to the spine unless otherwise noted.

As explained below, the bone stabilization devices 12 may be used afterlaminectomy, discectomy, artificial disc replacement, microdiscectomy,laminotomy and other applications for providing temporary or permanentstability in the spinal column. For example, lateral or central spinalstenosis may be treated with the bone fixation devices 12 and techniquesdescribed below. In such procedures, the bone fixation devices 12 andtechniques may be used alone or in combination with laminectomy,discectomy, artificial disc replacement, and/or other applications forrelieving pain and/or providing stability.

An embodiment of the stabilization device 12 will now be described indetail with initial reference to FIGS. 2-4. The stabilization device 12comprises a body 28 that extends between a proximal end 30 and a distalend 32. The length, diameter and construction materials of the body 28can be varied, depending upon the intended clinical application. Inembodiments optimized for spinal stabilization in an adult humanpopulation, the body 28 will generally be within the range of from about20-90 mm in length and within the range of from about 3.0-8.5 mm inmaximum diameter. The length of the helical anchor, discussed below, maybe about 8-80 millimeters. Of course, it is understood that thesedimensions are illustrative and that they may be varied as required fora particular patient or procedure.

In one embodiment, the body 28 comprises titanium. However, as will bedescribed in more detail below, other metals, or bioabsorbable ornonabsorbable polymeric materials may be utilized, depending upon thedimensions and desired structural integrity of the finishedstabilization device 12.

The distal end 32 of the body 28 is provided with a cancellous boneanchor and/or distal cortical bone anchor 34. Generally, for spinalstabilization, the distal bone anchor 34 is adapted to be rotationallyinserted into a portion (e.g., the pars or pedicle) of a first vertebra.In the illustrated embodiment, the distal anchor 34 comprises a helicallocking structure 72 for engaging cancellous and/or distal corticalbone. In the illustrated embodiment, the locking structure 72 comprisesa flange that is wrapped around a central core 73, which in theillustrated embodiment is generally cylindrical in shape. The flange 72extends through at least one and generally from about two to about 50 ormore full revolutions depending upon the axial length of the distalanchor 34 and intended application. The flange will generally completefrom about 2 to about 60 revolutions. The helical flange 72 ispreferably provided with a pitch and an axial spacing to optimize theretention force within cancellous bone. While the helical lockingstructure 72 is generally preferred for the distal anchor, it should beappreciated that the distal anchor could comprise other structuresconfigured to secure the device in the cancellous bone anchor and/ordistal cortical bone, such as, for example, various combinations andsub-combinations of hooks, prongs, expandable flanges, etc. See alsoe.g., U.S. Pat. No. 6,648,890, the entirety of which is herebyincorporated by reference herein.

The helical flange 72 of the illustrated embodiment has a generallytriangular cross-sectional shape (see FIG. 3B). However, it should beappreciated that the helical flange 72 can have any of a variety ofcross sectional shapes, such as rectangular, oval or other as deemeddesirable for a particular application through routine experimentationin view of the disclosure herein. For example, in one modifiedembodiment, the flange 72 has a triangular cross-sectional shape with ablunted or square apex. One particularly advantageous cross-sectionalshape of the flange are the blunted or square type shapes. Such shapescan reduce cutting into the bone as the proximal end of the device isactivated against causing a windshield wiper effect that can loosen thedevice 12. The outer edge of the helical flange 72 defines an outerboundary. The ratio of the diameter of the outer boundary to thediameter of the central core 73 can be optimized with respect to thedesired retention force within the cancellous bone and giving dueconsideration to the structural integrity and strength of the distalanchor 34. Another aspect of the distal anchor 34 that can be optimizedis the shape of the outer boundary and the central core 73, which in theillustrated embodiment are generally cylindrical.

The distal end 32 and/or the outer edges of the helical flange 72 may beatraumatic (e.g., blunt or soft). This inhibits the tendency of thestabilization device 12 to migrate anatomically distally and potentiallyout of the vertebrae after implantation. Distal migration is alsoinhibited by the dimensions and presence of a proximal anchor 50, whichwill be described below. In the spinal column, distal migration isparticularly disadvantageous because the distal anchor 34 may harm thetissue, nerves, blood vessels and/or spinal cord which lie within and/orsurround the spine. Such features also reduce the tendency of the distalanchor to cut into the bone during the “window-wiper effect” that iscaused by cyclic loading of the device as will be described. In otherembodiments, the distal end 32 and/or the outer edges of the helicalflange 72 may be sharp and/or configured such that the distal anchor 34is self tapping and/or self drilling.

A variety of other embodiments for the distal anchor 32 can also beused. For example, the various distal anchors described in U.S. Pat. No.6,908,465, issued Jun. 21, 2005 can be incorporated into thestabilization device 12 described herein. The entire contents of thisapplication are hereby expressly incorporated by reference. Inparticular, the distal anchor 32 may comprise a single helical threadsurrounding a lumen, much as in a conventional corkscrew. Alternatively,a double helical thread may be utilized, with the distal end of thefirst thread rotationally offset from the distal end of the secondthread. The use of a double helical thread can enable a greater axialtravel for a given degree of rotation and greater retention force than acorresponding single helical thread. Specific distal anchor designs canbe optimized for the intended use, taking into account desiredperformance characteristics, the integrity of the distal bone, andwhether the distal anchor is intended to engage exclusively cancellousbone or will also engage cortical bone. In still other embodiments, thedistal anchor 34 may be formed without a helical flange. For example,various embodiments of levers, prongs, hooks and/or radially expandabledevices may also be used. See e.g., U.S. Pat. No. 6,648,890, which ishereby expressly incorporated by reference in its entirety.

As shown in FIG. 3B, the body 28 is cannulated forming a central lumen42 to accommodate installation over a placement wire as is understood inthe art. The cross section of the illustrated central lumen is circularbut in other embodiments may be non circular, e.g., hexagonal, toaccommodate a corresponding male tool for installation or removal of thebody 28 as explained below. In other embodiments, the body 28 may bepartially or wholly solid.

With continued reference to FIGS. 2-4, the proximal end 30 of the body28 is provided with a rotational coupling 70, for allowing the body 28to be rotated. Rotation of the rotational coupling 70 can be utilized torotationally drive the distal anchor 32 into the bone. In suchembodiments, any of a variety of rotation devices may be utilized, suchas electric drills or hand tools, which allow the clinician to manuallyrotate the proximal end 30 of the body 28. Thus, the rotational coupling70 may have any of a variety of cross sectional configurations, such asone or more curved faces, flats, or splines. In the illustratedembodiment, the rotational coupling 70 is a male element in the form ofa hexagonal projection. However, in other embodiments, the rotationalcoupling 70 may be in the form of a female component, machined, milledor attached to the proximal end 30 of the body 28. For example, in onesuch embodiment, the rotational coupling 70 comprises an axial recesswith a polygonal cross section, such as a hexagonal cross section. Asexplained above, the axial recess may be provided as part of the centrallumen 42.

The proximal end 30 of the fixation device is also provided with aproximal anchor 50. The proximal anchor 50 comprises a housing 52, whichforms a lumen 53 (see FIG. 5) configured such that the body 28 mayextend, at least partially, through the proximal anchor 50. The proximalanchor 50 is axially distally moveable along the body 28 such that theproximal anchor 50 can be properly placed with respect to the inferiorvertebra and superior vertebra. As will be explained below,complimentary locking structures such as threads, levers, split rings,and/or ratchet like structures between the proximal anchor 50 and thebody 28 resist proximal movement of the anchor 50 with respect to thebody 28 under normal use conditions. The proximal anchor 50 preferablycan be axially advanced along the body 28 with and/or without rotationas will be apparent from the disclosure herein.

With particular reference to FIGS. 4-6, in the illustrated embodiment,the complementary structure of the proximal anchor 50 is formed by anannular ring 51, which is positioned within an annular recess 55 formedalong the lumen 53. As will be explained below, the ring 51 comprisessurface structures 54 which interact with complimentary surfacestructures 58 on the body 28. In the illustrated embodiment, thecomplimentary surface structures 58 comprise a series of annular ridgesor grooves 60 formed on the surface of the body 28. The surfacestructures 54 and complementary surface structures 58 permit distalaxial travel of the proximal anchor 50 with respect to the body 28, butresist proximal travel of the proximal anchor 50 with respect to thebody 28 as explained below.

As shown in FIG. 6, the annular ring 51 is split (i.e., has a least onegap) and is interposed between the body 28 and the recess 55 of theproximal anchor 50 (see FIG. 5). In the illustrated embodiment, the ring51 comprises a tubular housing 57 (see FIG. 6), which defines a gap orspace 59. In one embodiment, the gap 59 is defined by a pair of edges 61a, 61 b, that are generally straight and parallel to each other.Although not illustrated, it should be appreciated that in modifiedembodiments, the ring 51 can be formed without a gap. When the ring 51is positioned along the body 28, the ring 51 preferably surrounds asubstantial portion of the body 28. The ring 51 can be configured sothat the ring 51 can flex or move radially outwardly in response to anaxial force so that the ring 51 can be moved relative to the body 28, asdescribed below.

In the illustrated embodiment, the tubular housing 57 includes at leastone and in the illustrated embodiment ten teeth or flanges 63, which areconfigured to engage the complementary surface structures 58 on the body28 in a ratchet-like motion. In the illustrated embodiment (see FIG. 5),the teeth or flanges include a first surface 65 that lies generallyperpendicular to the longitudinal axis of the anchor and generally facesthe proximal direction (i.e., the direction labeled “P” in FIG. 5) and asecond surface 67 that is inclined with respect to the longitudinal axisof the anchor and that faces distal direction (i.e., the directionlabeled “D” in FIG. 5). It should be noted that the proximal anddirections in FIG. 5 are reversed with respect to FIG. 4.

With continued reference to FIG. 5, the recess 55 is sized anddimensioned such that as the proximal anchor 50 is advanced distallyover the body, the second surface 67 of the annular ring 51 can slidealong and over the complementary retention structures 58 of the body 28.That is, the recess 55 provides a space for the annular ring to moveradially away from the body 28 as the proximal anchor 50 is advanceddistally.

A distal portion 69 of the recess 55 is sized and dimensioned such thatafter the proximal anchor 50 is appropriately advanced, proximal motionof the proximal anchor 50 is resisted as the annular ring 51 becomeswedged between the body 28 and an angled engagement surface 71 of thedistal portion 69. In this manner, proximal movement of the proximalanchor 50 under normal use conditions may be prevented. In modifiedembodiments, the annular ring 51 can be sized and dimensioned such thatthe ring 51 is biased inwardly to engage the retention structures 58 onthe body 28. The bias of the annular ring 51 can result in a moreeffective engagement between the complementary retention structures 58of the body and the retention structures 54 of the ring 51.

In certain embodiments, it is advantageous for the outer surface 49 ofthe proximal anchor 50 to rotate with respect to the body 28. Thisarrangement advantageously reduces the tendency of the body 28 to rotateand/or move within the superior articular process of the inferiorvertebrae 10 a as the outer surface 49 contacts, abuts or wedges againstthe inferior articular process of the superior vertebrae 10 b. In theillustrated embodiment, rotation of the outer surface 49 is provided byconfiguring the lumen 53 and annular recess 55 such that the anchor 50can rotate about the body 28 and ring 51. Preferably, as the anchor 50rotates the axial position of the anchor 50 with respect to the body 28remains fixed. That is, the annular ring 51 resists proximal travel ofthe proximal anchor 50 with respect to the body 28 while the anchor 50is permitted to rotate about the body 28 and ring 51. Of course those ofskill in the art will recognize other configurations and mechanisms(e.g., bearings, rollers, slip rings, etc.) for providing rotation ofthe outer surface 49 with respect to the body 28. In a modifiedembodiment, the proximal anchor 50 can be configured such that it doesnot rotate with respect to the body 28. In such an embodiment, a key orone or more anti-rotational features (e.g., splines, grooves, flatsides, etc.) can be provided between the proximal anchor 50, the ring 51and/or the body 51 to limit or prevent rotation of the proximal anchor50 with respect to the body 28.

As mentioned above, it is contemplated that various other retentionstructures 54 and complementary retention structures 58 may be usedbetween the body 28 and the proximal anchor 50 to permit distal axialtravel of the proximal anchor 50 with respect to the body 28, but resistproximal travel of the proximal anchor 50 with respect to the body 28.Examples of such structures can be found in U.S. Pat. No. 6,685,706,entitled “PROXIMAL ANCHORS FOR BONE FIXATION SYSTEM.” The entirecontents of U.S. Pat. No. 6,685,706 are hereby expressly incorporated byreference herein. In such embodiments, the structures 54 andcomplementary retention structures 58 can be configured to allow theproximal anchor to be advanced with or without rotation with respect tothe body 28.

As mentioned above, the complimentary surface structures 58 on the body28 comprise threads, and/or a series of annular ridges or grooves 60.These retention structures 58 are spaced axially apart along the body28, between a proximal limit 62 and a distal limit 64. See FIG. 4. Theaxial distance between proximal limit 62 and distal limit 64 is relatedto the desired axial working range of the proximal anchor 50, and thusthe range of functional sizes of the stabilization device 12. Thus, thestabilization device 12 of the example embodiment can provide accurateplacement between the distal anchor 34 and the proximal anchor 50throughout a range of motion following the placement of the distalanchor in a vertebra. That is, the distal anchor 34 may be positionedwithin the cancellous and/or distal cortical bone of a vertebra, and theproximal anchor may be distally advanced with respect to the distalanchor throughout a range to provide accurate placement of the proximalanchor 50 with respect to the vertebra without needing to relocate thedistal anchor 34 and without needing to initially locate the distalanchor 34 in a precise position with respect to the proximal side of thebone or another vertebra. The arrangement also allows the compressionbetween the distal anchor 34 and the proximal anchor 50 to be adjusted.Providing a working range throughout which positioning of the proximalanchor 50 is independent from setting the distal anchor 34 allows asingle device to be useful for a wide variety of different anatomies, aswell as eliminates or reduces the need for accurate device measurement.In addition, this arrangement allows the clinician to adjust thecompression force during the procedure without adjusting the position ofthe distal anchor. In this manner, the clinician may focus onpositioning the distal anchor sufficiently within the vertebra to avoidor reduce the potential for distal migration out of the vertebra, whichmay damage the particularly delicate tissue, blood vessels, nervesand/or spinal cord surrounding or within the spinal column. In additionor alternative, the above described arrangement allows the clinician toadjust the positioning of the proximal anchor 50 with respect to theinferior articular process of the superior adjacent vertebrae. In thismanner, the clinician may adjust the position of the proximal anchor 50without adjusting the position of the distal anchor such that the anchor50 is configured to wedge or abut against inferior articular process ofthe superior adjacent vertebrae. In a modified embodiment, the positionof the proximal anchor 50 with respect to the surrounding vertebra canbe adjusted by rotating the device 12 and advancing the distal anchorand the proximal anchor carried by the body.

In the embodiment of FIGS. 4-6, the proximal anchor 50 can be distallyadvanced over the body 28 without rotating the proximal anchor 50 withrespect to the body 28. In one embodiment, the ring 51 and the proximalanchor 50 are rotationally linked by, for example, providinginter-engaging structures (e.g., tabs, ridges and the like). In such anembodiment, the proximal anchor 50 can be advanced without rotating theproximal anchor 50 and be removed and/or the position adjusted in aproximal or distal direction by rotating the proximal anchor withrespect to the body 28. This can allow the surgeon to remove an proximalanchor and use a different sized or configured proximal anchor 50 if thefirst proximal anchor is determined to be inadequate. In such anembodiment, the proximal anchor 50 is preferably provided with one ormore engagement structures (e.g., slots, hexes, recesses, protrusions,etc.) configured to engage a rotational and/or gripping device (e.g.,slots, hexes, recesses, protrusions, etc.). Thus, in some embodiments,the proximal anchor 50 can be pulled and/or rotated such that the anchor50 is removed from the body.

In many applications, the working range is at least about 10% of theoverall length of the device, and may be as much as 20% or 50% or moreof the overall device length. In the context of a spinal application,working ranges of up to about 10 mm or more may be provided, sinceestimates within that range can normally be readily accomplished withinthe clinical setting. The embodiments disclosed herein can be scaled tohave a greater or a lesser working range, as will be apparent to thoseof skill in the art in view of the disclosure herein.

In embodiments optimized for spinal stabilization in an adult humanpopulation, the anchor 50 will have a diameter within the range of fromabout 1 to 1/16 of an inch in another embodiment the proximal anchorproximal anchor 50 within the range from about 0.5 to ⅛ of an inch inanother embodiment.

With reference back to FIGS. 2-4, in the illustrated embodiment, theouter surface 49 of the proximal anchor 50 has a smooth or sphericalshape. As will be explained below, the outer surface 49 of the proximalanchor 50 is configured to abut against the inferior facet of thesuperior adjacent vertebrae. In this manner, motion between the adjacentvertebrae may be limited and/or constrained.

FIG. 7A illustrates an embodiment in which the body 28 comprises a firstportion 36 and a second portion 38 that are coupled together at ajunction 40. In the illustrated embodiment, the first portion 36 carriesthe distal anchor 34 (shown without a central core) while the secondportion 38 forms the proximal end 30 of the body 28. As will beexplained in more detail below, in certain embodiments, the secondportion 38 may be used to pull the body 28 and therefore will sometimesbe referred to as a “pull-pin.” The first and second portions 36, 38 arepreferably detachably coupled to each other at the junction 40. In theillustrated embodiment, the first and second portions 36, 38 aredetachably coupled to each other via interlocking threads.

Specifically, as best seen in FIG. 7B, the body 28 includes an innersurface 41, which defines a central lumen 42 that preferably extendsfrom the proximal end 30 to the distal end 32 throughout the body 28. Atthe proximal end of the first portion 36, the inner surface 41 includesa first threaded portion 44. The first threaded portion 44 is configuredto mate with a second threaded portion 46, which is located on the outersurface 45 of the second portion 38. The interlocking annular threads ofthe first and second threaded portions 44, 46 allow the first and secondportions 36, 38 to be detachably coupled to each other. In one modifiedembodiment, the orientation of the first and second threaded portions44, 46 can be reversed. That is, the first threaded portion 44 can belocated on the outer surface of the first portion 36 and the secondthreaded portion 46 can be located on the inner surface 41 at the distalend of the second portion 38. Any of a variety of other releasablecomplementary engagement structures may also be used, to allow removalof second portion 38 following implantation, as is discussed below.

In a modified arrangement, the second portion 38 can comprise any of avariety of tensioning elements for permitting proximal tension to beplaced on the distal anchor 34 while the proximal anchor is advanceddistally. For example, any of a variety of tubes or wires can beremovably attached to the first portion 36 and extend proximally to theproximal handpiece. In one such arrangement, the first portion 36 caninclude a releasable connector in the form of a latching element, suchas an eye or hook. The second portion 38 can include a complementaryreleasable connector (e.g., a complementary hook) for engaging the firstportion 36. In this manner, the second portion 38 can be detachablycoupled to the first portion 36 such proximal traction can be applied tothe first portion 36 through the second portion as will be explainedbelow. Alternatively, the second portion 48 may be provided with an eyeor hook, or transverse bar, around which or through which a suture orwire may be advanced, both ends of which are retained at the proximalend of the device. Following proximal tension on the tensioning elementduring the compression and/or positioning step, one end of the suture orwire is released, and the other end may be pulled free of the device.Alternate releasable proximal tensioning structures may be devised bythose of skill in the art in view of the disclosure herein.

In a final position, the distal end of the proximal anchor 50 preferablyextends distally past the junction 40 between the first portion 36 andthe second portion 38. As explained above, the proximal anchor 50 isprovided with one or more surface structures 54 for cooperating withcomplementary surface structures 58 on the first portion 36 of the body28.

In this embodiment, the stabilization device 12 may include anantirotation lock (not shown) between the first portion 36 of the body28 and the proximal collar 50. For example, the first portion 36 mayinclude one or more of flat sides (not shown), which interact withcorresponding flat structures in the proximal collar 50. As such,rotation of the proximal collar 50 is transmitted to the first portion36 and distal anchor 34 of the body 28. Of course, those of skill in theart will recognize various other types of splines or other interfitstructures can be used to prevent relative rotation of the proximalanchor and the first portion 36 of the body 28. To rotate the proximalanchor 50, the housing 52 may be provided with a gripping structure (notshown) to permit an insertion tool to rotate the flange proximal anchor50. Any of a variety of gripping structures may be provided, such as oneor more slots, recesses, protrusions, flats, bores or the like. In oneembodiment, the proximal end of the proximal anchor 50 is provided witha polygonal, and, in particular, a pentagonal or hexagonal recess orprotrusion.

Methods implanting stabilization devices described above as part of aspinal stabilization procedure will now be described. Although certainaspects and features of the methods and instruments described herein canbe utilized in an open surgical procedure, the disclosed methods andinstruments are optimized in the context of a percutaneous or minimallyinvasive approach in which the procedure is done through one or morepercutaneous small openings. Thus, the method steps which follow andthose disclosed are intended for use in a trans-tissue approach.However, to simplify the illustrations, the soft tissue adjacent thetreatment site have not been illustrated in the drawings.

In one embodiment of use, a patient with a spinal instability isidentified. The patient is preferably positioned face down on anoperating table, placing the spinal column into a normal or flexedposition. A trocar optionally may then be inserted through a tissuetract and advanced towards a first vertebra. In another embodiment,biopsy needle (e.g., Jamshidi™) device can be used. A guidewire may thenbe advanced through the trocar (or directly through the tissue, forexample, in an open surgical procedure) and into the first vertebrae.With reference to FIG. 1D, the guide wire 110 is preferably insertedinto the pedicle of the vertebrae preferably through the pars (i.e. theregion of the lamina between the superior and inferior articularprocesses).

With reference to FIG. 1E, a suitable expandable access sheath ordilator 112 can then be inserted over the guidewire and expanded (FIG.1F) to enlarge the tissue tract and provide an access lumen forperforming the methods described below in a minimally invasive manner.In a modified embodiment, a suitable tissue expander (e.g., a balloonexpanded catheter or a series of radially enlarged sheaths) can beinserted over the guidewire and expanded to enlarge the tissue tract. Asurgical sheath can then be advanced over the expanded tissue expander.The tissue expander can then be removed such that the surgical sheathprovides an enlarged access lumen. Any of a variety of expandable accesssheaths or tissue expanders can be used, such as, for example, a balloonexpanded catheter, a series of radially enlarged sheaths inserted overeach other, and/or the dilation introducer described in U.S. patentapplication Ser. No. 11/038,784, filed Jan. 19, 2005 (Publication No.2005/0256525), the entirety of which is hereby incorporated by referenceherein.

A drill with a rotatable tip may be advanced over the guidewire andthrough the sheath. The drill may be used to drill an opening in thevertebrae. The opening may be configured for (i) for insertion of thebody 28 of the bone stabilization device 12, (ii) tapering and/or (iii)providing a counter sink for the proximal anchor 50. In otherembodiments, the step of drilling may be omitted. In such embodiments,the distal anchor 34 is preferably self-tapping and self drilling. Inembodiments, in which an opening is formed, a wire or other instrumentmay be inserted into the opening and used to measure the desired lengthof the body 28 of the device 12.

The body 28 of the fixation device may be advanced over the guidewireand through the sheath until it engages the vertebrae. The body 28 maybe coupled to a suitable insertion tool prior to the step of engagingthe fixation device 12 with the vertebrae. The insertion tool may beconfigured to engage the coupling 70 on the proximal end of the body 28such that insertion tool may be used to rotate the body 28. In such anembodiment, the fixation device 12 is preferably configured such that itcan also be advanced over the guidewire.

The insertion tool may be used to rotate the body 28 thereby driving thedistal anchor 34 to the desired depth within the pedicle of thevertebra. The proximal anchor 50 may be carried by the fixation deviceprior to advancing the body 28 into the vertebra, or may be attachedand/or coupled to the body 28 following placement (partially or fully)of the body 28 within the vertebrae. In another embodiment, the anchor50 may be pre-attached and/or coupled to the body 28.

In one embodiment, the clinician will have access to an array of devices12, having, for example, different diameters, axial lengths,configurations and/or shapes. The clinician will assess the position ofthe body 28 with respect to the superior vertebrae and choose the device12 from the array, which best fits the patient anatomy to achieve thedesired clinical result. In another embodiment, the clinician will haveaccess to an array of devices 12, having, for example, bodies 28 ofdifferent diameters, axial lengths. The clinician will also have anarray of proximal anchors 50, having, for example, differentconfigurations and/or shapes. The clinician will choose the appropriatebody 28 and then assess the position of the body 28 with respect to thesuperior vertebrae and choose the proximal anchor 50 from the array,which best fits the patient anatomy to achieve the desired clinicalresult. In such an embodiment, the proximal anchor 50 is advantageouslycoupled to body 28 after the body 28 is partially or fully inserted intothe vertebrae.

Once the distal anchor 34 is in the desired location, the proximalanchor 50 is preferably advanced over the body 28 until it reaches itsdesired position. This may be accomplished by pushing on the proximalanchor 50 or by applying a distal force to the proximal anchor 50. Inanother embodiment, the proximal anchor 50 is advanced by applying aproximal retraction force to the proximal end 30 of body 28, such as byconventional hemostats, pliers or a calibrated loading device, whiledistal force is applied to the proximal anchor 50. In this manner, theproximal anchor 50 is advanced distally with respect to the body 28until the proximal anchor 50 is in its proper position (e.g., positionedsnugly against the outer surface of the vertebra). Appropriatetensioning of the stabilization device 12 can be accomplished by tactilefeedback or through the use of a calibration device for applying apredetermined load on the stabilization device 12. As explained above,one advantage of the structure of the illustrated embodiments is theability to adjust the compression and/or the position of the proximalanchor 50 independently of the setting of the distal anchor 34 withinthe vertebra. For example, the positioning of the distal anchor 34within the vertebra can be decoupled from the positioning of theproximal anchor 50 with respect to the superior vertebra.

In one embodiment, the proximal anchor 50 is pushed over the body 28 bytapping the device with a slap hammer or similar device that can be usedover a guidewire. In this manner, the distal end of the device 12 isadvantageously minimally disturbed, which prevents (or minimizes) thethreads in the bore from being stripped.

Following appropriate tensioning of the proximal anchor 50, the proximalportion of the body 28 extending proximally from the proximal anchor 50can be removed. In one embodiment, this may involve cutting the proximalend of the body 28. For example, the proximal end of the body may beseparated by a cutting instrument or by cauterizing. Cauterizing mayfuse the proximal anchor 50 to the distal end 32 of the body 28 therebyadding to the retention force between the proximal anchor 50 and thebody 28. Such fusion between the proximal anchor and the body may beparticularly advantageous if the pin and the proximal anchor are madefrom a polymeric or plastic material. In this manner, as the material ofthe proximal anchor and/or the pin is absorbed or degrades, the fusioncaused by the cauterizing continues to provide retention force betweenthe proximal anchor and the body. In another embodiment, the bodycomprises a first and a second portion 36, 38 as described above. Insuch an embodiment, the second portion 38 may detached from the firstportion 36 and removed. In the illustrated embodiment, this involvesrotating the second portion 38 with respect to the first portion via thecoupling 70. In still other embodiments, the proximal end of the body 28may remain attached to the body 28.

The access site may be closed and dressed in accordance withconventional wound closure techniques and the steps described above maybe repeated on the other side of the vertebrae for substantial bilateralsymmetry as shown in FIGS. 1A and 1B. The bone stabilization devices 12may be used alone or in combination with other surgical procedures suchas laminectomy, discectomy, artificial disc replacement, and/or otherapplications for relieving pain and/or providing stability.

As will be described in detail below, the dynamic stabilization device12 can provide adjacent level support as an adjunct to fusion therapy.In one embodiment, the fusion therapy involves the fixation device 800,which will be described in detail below. The fixation device 800 can bepositioned below (or above in other embodiments) the stabilizationdevice 12 and can be used to promote spinal fusion below the spinallevel at which motion is limited by the dynamic stabilization device. Inother embodiments, fusion can be promoted using other devices.

As will be explained below, the superior body structure (e.g., thesuperior vertebrae 10 b) can be conformed to the device by providing acomplementary surface or interface. In one embodiment, the superiorvertebrae can be modified using a separate drill or reamer that is alsoused to form the countersink 200 described above. In other embodiments,the drill that is used to form an opening in the inferior body can beprovided with a countersink portion that is also used to modify theshape of the superior vertebrae 10 b. In still other embodiments, theshape of the superior vertebrae 10 b can be modified using files, burrsand other bone cutting or resurfacing devices to form a complementarysurface or interface for the proximal anchor 50.

As mentioned above, a countersink can be provided for the proximalanchor 50. With reference to FIG. 8, a pair of counter sinks 200 isshown formed in or near the pars of the inferior vertebrae 10 a. Eachcounter sink 200 is preferably configured to generally correspond to adistal facing portion 49 a (see FIG. 4 or FIG. 10A) of the proximalanchor 50. In this manner, the proximal anchor 50, in a final position,may be seated at least partially within the inferior vertebrae 10 a. Inthe illustrated embodiment, the countersink 200 has a generallyspherical configuration that corresponds generally to the sphericalshape of the distal portion 49 a of the proximal anchor 50 of theillustrated embodiment. In modified embodiments, the countersink 200 canhave a modified shape (e.g., generally cylindrical, conical,rectangular, etc.) and/or generally configured to correspond to thedistal portion of a proximal anchor 50 with a different shape than theproximal anchor illustrated in FIGS. 2-4.

The countersink 200 advantageously disperses the forces received by theproximal anchor 50 by the superior vertebrae 10 b and transmits saidforces to the inferior vertebrae 10 a. As will be explained in moredetail below, the countersink 200 can be formed by a separate drillinginstrument or by providing a counter sink portion on a surgical drillused to from a opening in the body 10 b.

In addition or in the alternative to creating the countersink 200, theshape of the inferior articular process IAP (which can include the facetin certain embodiments) of the superior vertebrae 10 b may be modifiedin order to also disperse the forces generated by the proximal anchor 50contacting, abutting and/or wedging against the superior vertebrae 10 b.For example, as shown in FIG. 8, a portion 204 of the inferior articularprocess IAP of the superior vertebrae 10 b that generally faces theproximal anchor 50 can be removed with the goal of dispersing and/orreducing the forces applied to the proximal anchor 50. In theillustrated embodiment, the inferior articular process is provided witha generally rounded recess 206 that corresponds generally to the roundedouter surface 49 of the proximal anchor 50. In modified embodiments, theinferior articular process IAP can be formed into other shapes in lightof the general goal to reduce and/or disperse the forces applied to theproximal anchor 50. For example, in certain embodiments, the inferiorarticular process IAP may be formed into a generally flat, blunt orcurved shape. In other embodiments, the inferior articular process IAPmay be configured to abut and/or wedge more efficiently with a proximalanchor 50 of a different shape (e.g., square, oval, etc.). In general,the countersink 200 and surface 206 provide for an increased contactsurface between the superior vertebra and the proximal anchor 50 and theinferior vertebra and the proximal anchor 50. This contact area reducesstress risers in the device and the associated contact areas of thevertebrae. In addition, the windshield wiper affect is reduced as theforces transmitted to the proximal anchor 50 from the superior vertebraeare transmitted through the area formed by the countersink 200.

FIGS. 9A and 9B illustrate an exemplary embodiment of a device 210 thatcan be used to form the countersink 200 and/or the recess 206 describedabove. As shown, the device comprises a body 212 having a distal end214, a proximal end 216 and a guidewire lumen (not shown) extendingtherethrough. The proximal end 216 is configured to engage any of avariety of standard driving tools as is known in the art. The distal end214 is provided with an outer surface 220 that generally corresponds tothe outer surface 49 of the proximal anchor 50. The outer surface 220 isalso provided with one or more removal or cutting features 218 (e.g.,flutes, sharp edges, etc.) so as to remove or cut bone as the device 210is rotated. A pin 221 (shown in dashed lines in FIG. 9B) can be providedat the end of the device 210. The pin 221 can be inserted into the holeformed in the vertebrae and helps to center and support the device 221at it cuts the countersink 200 and/or recess 206 into the bone.

In use, the device 210 is advanced over a guidewire that is insertedinto the inferior vertebrae 10 b. As the device 210 is advanced androtated, the device 210 encounters the inferior process IAP (see FIG. 8)of the superior vertebrae 10 b and portions thereof are removed. Furtheradvancement of the device 210, forms the countersink 200 in the superiorarticular process of the inferior vertebrae 10 a and removes additionalportions of the superior vertebrae 10 b. Accordingly, in thisembodiment, the device 210 can be used to form both the countersink 200and to change the shape of the inferior articular process IAP of thesuperior vertebrae 10 b.

FIGS. 9C-E illustrate an insertion tool 300 that may be used to rotateand insert the body 28 as described above. As shown, the tool 300generally comprises an elongated shaft 302 having a distal end 304, aproximal end 306 and a guidewire lumen 308 extending there through. Inthe illustrated embodiment, the proximal end 304 includes a flat edge310 and engagement feature 312 for engaging a driving tool (e.g., adrill). In modified embodiments, the proximal end 306 can include ahandle such that the tool 300 can be rotated manually.

The distal end 304 of the tool 306 is provided with a distal sleeveportion 314, which has an outer shape that preferably correspondssubstantially to the outer surface shape of the proximal anchor used inthe procedure. Within the distal sleeve portion 314 is a lumen 316,which communicates with the guidewire lumen 308 and is configured toreceive the proximal end of the body 28. The lumen 316 includes arotational region 318 configured to engage the coupling 70 on theproximal end of the body 28. Distal to the rotational region 318 is arecess 320 in which an elastic or resilient member 322 (e.g., a siliconsleeve) can be placed. As shown in FIG. 9E, when the proximal end of thebody 28 is inserted into the lumen 316, the rotational region 318engages the coupling 70 and the elastic or reslilent member 322 gripsthe body 28 to hold the body 28 in place within the tool 300.

As described above, the insertion tool 300 may be used to rotate thebody 28 thereby driving the distal anchor 34 to the desired depth withinthe pedicle of the vertebrae. The surgeon can stop rotating the body 28before the distal end of the tool 300 contacts the bone. In embodiments,in which a countersink is formed, the tool 300 can be rotated until thedistal end sits within the countersink at which point further rotationof the tool 300 will not cause the distal anchor to advance further asfurther advancement of the body 28 causes it to be released from thetool 300. In this manner, over advancement of the distal anchor 32 intothe vertebrae can be prevented or limited.

It should be appreciated that not all of the steps described above arecritical to procedure. Accordingly, some of the described steps may beomitted or performed in an order different from that disclosed. Further,additional steps may be contemplated by those skilled in the art in viewof the disclosure herein, without departing from the scope of thepresent inventions.

With reference to FIGS. 1A and 1B, the proximal anchors 50 of thedevices 12 extend above the pars such that they abut against theinferior facet of the superior adjacent vertebrae. In this manner, theproximal anchor 50 forms a wedge between the vertebra limitingcompression and/or extension of the spine as the facet of the superioradjacent vertebrae abuts against the proximal anchor 50. In this manner,extension is limited while other motion is not. For example, flexion,lateral movement and/or torsion between the superior and inferiorvertebra is not limited or constrained at least to the degree of theextension. In this manner, the natural motion of the spine can bepreserved, especially for those patients with mild or moderate discconditions. Preferably, the devices are implantable through a minimallyinvasive procedure and, more preferably, through the use of smallpercutaneous openings as described above. In this manner, the high cost,lengthy in-patient hospital stays and the pain associated with openprocedures can be avoided and/or reduced. In one embodiment, the devices12 may be removed and/or proximal anchors 50 may be removed in asubsequent procedure if the patient's condition improves. Onceimplanted, it should be appreciated that, depending upon the clinicalsituation, the proximal anchor 50 may be positioned such that itcontacts surfaces of the adjacent vertebrae all of the time, most of thetime or only when movement between the adjacent vertebrae exceeds alimit.

In some instances, the practitioner may decide to use a more aggressivespinal fixation or fusion procedure after an initial period of using thestabilization device 12. In one particular embodiment, the bonestabilization device 12 or a portion thereof may be used as part of thespinal fixation or fusion procedure. In one such application, theproximal anchor 50 can be removed from the body 28. The body 28 canremain in the spine and used to support a portion of a spinal fixationdevice. For example, the body 28 may be used to support a fixation rodthat is coupled to a device implanted in a superior or inferiorvertebrae. Examples of such fusion systems can be found in U.S. patentapplication Ser. No. 10/623,193, filed Jul. 18, 2003 (U.S. PatentPublication No. 2004/0127906), the entirety of which is herebyincorporated by reference herein. Such a device is also described below.

As mentioned above, in certain embodiments described above, it may beadvantageous to allow the proximal anchor to rotate with respect to thebody 28 thereby preventing the proximal anchor 50 from causing thedistal anchor 34 from backing out of the pedicle. In another embodiment,engagement features (as described below) may be added to the proximalanchor 50 to prevent rotation of the proximal anchor 50.

FIG. 1C illustrates a modified embodiment in which the first and secondfixation devices 12 a, 12 b are coupled together by a member 5 thatextends generally around or above the spinous process of the superiorvertebra 10 b. In this manner, the member 5 can be used to limit flexionof the spinal column. The member may comprise any of a variety ofsuitable structural members. In one embodiment, the member comprises asuture or wire that is tied to the proximal end of the bodies 28 or theproximal anchor. In certain embodiments, various hooks or eyelets can beprovided on the body or proximal anchor to facilitate coupling themember to the devices 12 a, 12 b.

The fixation devices 12 described herein may be made from conventionalnon-absorbable, biocompatible materials including stainless steel,titanium, alloys thereof, polymers, composites and the like andequivalents thereof. In one embodiment, the distal anchor comprises ametal helix, while the body and the proximal anchor comprise abioabsorbable material. Alternatively, the distal anchor comprises abioabsorbable material, and the body and proximal anchor comprise eithera bioabsorbable material or a non-absorbable material.

In one embodiment, the proximal anchor 50 is formed, at least in part,from an elastic and/or resilient material. In this manner, the shock andforces that are generated as the proximal anchor abuts or wedges againstthe inferior articular process of the superior adjacent vertebrae can bereduced or dissipated. In one such embodiment, the proximal anchor 50 isformed in part by a polycarbonate urethane or a hydrogel. In suchembodiments, the elastic material may be positioned on the outersurfaces of the proximal anchor or the portions of the outer surfacesthat abut against the surfaces of the inferior articular process of thesuperior adjacent vertebrae. In one embodiment, such an anchor has amodulus of elasticity that is lower than that of metal (e.g., titanium).In another embodiment, the modulus of elasticity can be substantiallyclose to that of bone. In yet another embodiment, the modulus ofelasticity can be less than that of bone. In this manner, the stressrisers generated during cyclic loading can be reduced to thereby reducethe tendency of the inferior articular process and the inferiorvertebrae to crack during cyclic loading.

For example, FIGS. 10A and 10B illustrate an embodiment of device 12′with a proximal anchor 50′ that comprises an outer housing or shell 402.The shell 402 may be formed or a resilient material such as, forexample, a biocompatible polymer. The proximal anchor 50′ also comprisesan inner member 404 that comprises a tubular housing 406 and a proximalflange 408. The inner member 402 is preferably formed of a harder morerugged material as compared to the shell 402, such as, for example,titanium or another metallic material. The shell 402 is fitted or formedover the tubular housing 406. When deployed, the shell 402 is held inplace between the flange 408 and the surface of the vertebrae in whichthe body 402 is placed. In modified embodiments, the shell 402 may becoupled to the inner member 404 in a variety of other manners, such as,adhesives, fasteners, interlocking surfaces structures and the like. Inthe illustrated embodiment, the inner member 404 includes a locking ring51 positioned within a recess 55 as described above. Of course, inmodified embodiments, other retention structures 54 and complementaryretention structures 58 may be used between the body 28 and the proximalanchor 50′ to permit distal axial travel of the proximal anchor 50′ withrespect to the body 28, but resist proximal travel of the proximalanchor 50′ with respect to the body 28.

In the illustrated embodiment of FIGS. 10A and 10B, the distal anchor 34is provided with atraumatic or blunt tip 7. In addition, the flange 72of the distal anchor 34 includes a square or blunt edges. These featuresreduce the tendency of the distal anchor to cut into the bone during thewindshield-wiper effect that may be caused by cyclic loading of thedevice as described above.

In another embodiment, the proximal anchor 50 is provided with amechanically resilient structure. Thus, as with the previous embodiment,the shock and forces that are generated as the proximal anchor abuts orwedges against the inferior articular process of the superior adjacentvertebrae can be reduced or dissipated. In one such embodiment, theproximal anchor 50 is provided with mechanical springs, lever armsand/or the like. In such embodiments, as the mechanically resilientstructure is compressed or extended the shock and forces are reduced ordissipated.

For example, FIGS. 11A-13B illustrate embodiments of a proximal anchor500, which comprises a tubular housing 502, which includes a recess 503for receiving a locking ring 51 as described above. The distal end 504of the housing 502 forms a generally rounded, semi-spherical face thatcan be inserted into a corresponding counter sink 200 (see FIG. 8) asdescribe above. Extending from the housings 502 are a plurality of leverarms or deflectable flanges 510. Each arm 510 generally comprises agenerally radially extending portion 512 and a generally circumferentialextending portion 514. In the illustrated embodiments, two (FIGS.13A-B), three (FIGS. 12A-B) and five arms (FIGS. 11A-B) are shown.However, the anchor 500 can include different numbers of arms (e.g.,one, four or greater than five arms). As the superior adjacent vertebrae10 b moves against the proximal anchor 500 the radially extendingportion 514 deflects relative to the tubular housing 502 to absorb ordisperse the forces generated by the contact.

As mentioned above, in the illustrated embodiment, the tubular member502 includes a locking ring 51 positioned within a recess 503 asdescribed above. Of course, in modified embodiments, other retentionstructures and complementary retention structures may be used betweenthe body 28 and the proximal anchor 500 to permit distal axial travel ofthe proximal anchor 500 with respect to the body 28, but resist proximaltravel of the proximal anchor 500 with respect to the body 28.

With reference to FIG. 14, in a modified embodiment, a distal end of aproximal anchor 50′ may include one or more bone engagement features100, which in the illustrated embodiment comprises a one or more spikes102 positioned on a contacting surface 104 of the proximal anchors. Thespikes 102 provide additional gripping support especially when theproximal anchor 50′ is positioned against, for example, uneven bonesurfaces and/or soft tissue. In addition, the spikes 102 may limitrotation of the proximal anchor 50′ with respect to the body 28 therebypreventing the proximal anchor 50′ from backing off the body 28. Otherstructures for the bone engagement feature 100 may also be used, suchas, for example, ridges, serrations, etc.

FIGS. 15 and 16 illustrate modified shapes of the proximal anchor whichcan be used alone or in combination with the elastic or resilientmaterial described above. In FIG. 15, a proximal anchor 50″ has a saddleshaped curved surface 51″ that generally faces the inferior articularprocess of the superior adjacent vertebra. In this embodiment, thesaddle shaped surface may limit compression and/or extension of theadjacent vertebra and limit side to side motion and/or torsion betweenthe vertebrae. FIG. 16 illustrates an embodiment in which a proximalanchor 50′″ has a rectangular shape with a flat shaped surface 51′″. Inthis embodiment, the flat shaped surface may limit compression and/orextension of the adjacent vertebra and limit side to side motion betweenthe vertebrae. In the embodiments of FIGS. 15 and 16, it may beadvantageous to limit or eliminate any rotation of the proximal anchor50″ and 50′″ with respect to the body 28 and/or the vertebra. As such,the proximal anchor 50″ and 50′″ can include the retention devices 100described above with reference to FIG. 14.

As mentioned above, in certain embodiments, clinician will also have anarray of proximal anchors 50′, 50″, and 50′″, having, for example,different configurations and/or shapes. The clinician will choose theappropriate body 28 and then assess the position of the body 28 withrespect to the superior vertebrae and chose a proximal anchor from thearray, which best fits the patient anatomy to achieve the desiredclinical result. In such an embodiment, the proximal anchor can beadvantageously coupled to body 28 after the body 28 is partially orfully inserted into the vertebrae. The clinician may also be providedwith an array of devices for forming differently sized or shapedcountersinks corresponding to the different proximal anchors.

As described above, in one embodiment, the proximal anchor 50 (which canalso refer to any or all of 50′, 50″, or 50′″) is configured such thatit can be removed after being coupled and advance over the body 28. Inthis manner, if the clinician determines after advancing the proximalanchor that the proximal anchor 50 is not of the right or mostappropriate configuration (e.g., size and/or shape), the clinician canremove the proximal anchor 50 and advance a different proximal anchor 50over the body 28. In such an embodiment, the proximal anchor 50 ispreferably provided with one or more engagement structures (e.g., slots,hexes, recesses, protrusions, etc.) configured to engage a rotationaland/or gripping device (e.g., slots, hexes, recesses, protrusions,etc.). Thus, in some embodiments, the proximal anchor 50 can be pulledand/or rotated such that the anchor 50 is removed from the body 28.

FIGS. 17 and 18 illustrate an embodiment of a tool 600 that can be usedto insert a proximal anchor 50 that utilizes a locking ring 51 (asdescribed above) onto a body 28 of the device 12. In the illustratedembodiment, the tool 600 comprises an elongated body 602 having a distalend 604 and a proximal end 606. The proximal end 606 is provided with ahandle 608 for manipulating the tool 600. The distal end 604 of thedevice is generally tubular and is coupled to or otherwise attached to adistal sleeve 610. The distal sleeve defines a chamber 611, whichextends from the distal end 604 of the elongated body 602 to the distalend 613 of the sleeve 610. A guidewire lumen 612 can extend through thetool 600.

With particular reference to FIG. 18, a pin 616 is partially positionedwithin the chamber 611. The pin 616 includes an enlarged proximalportion 618, which is positioned in the chamber 611. The pin 616 alsoincludes a reduced diameter portion 620, which extends outside thechamber 611. A guidewire lumen 622 can also extend through the pin 616such that the entire tool 600 can be inserted over a guidewire. Abiasing member 624 is positioned between the distal end 604 of thetubular member 602 the proximal end 618 of the pin 616. In this manner,the pin 616 is biased to the position shown in FIG. 18. Advantageously,the distal end 620 of the pin 616 has an outside diameter that isslightly larger than the inner diameter of the locking ring 51 (seee.g., FIG. 10B). Accordingly, the distal end 620 of the pin 616 can beinserted into the proximal anchor through its proximal end. In oneembodiment, the locking ring 51 grasps the distal end 620 of the pin 616to couple the proximal anchor 50 to the pin 616. In the loaded position,the proximal end of the proximal anchor 50 preferably contacts thedistal end 613 of the distal sleeve 610.

In use, the tool 600 is coupled to the proximal anchor as describedabove. After the body 28 is inserted into the vertebrae, the tool 600can be used to position the proximal anchor 50 over the proximal end ofthe body 28. The tool 600 is then advanced forward. As the tool 600 isadvanced forward, the proximal anchor 50 is pushed onto the body 28 asthe pin 616 retracts into the chamber 611. In this manner, the pin 616holds the locking ring 51 in an expanded position until it engages thebody 28. Once the pin 616 is fully retracted into the chamber 611, thepin 616 is decoupled from the proximal anchor 50 and the proximal anchor50 is fully coupled to the body 28.

In another embodiment, a dimension of the proximal anchor is capable ofbeing adjusted. For example, FIG. 19 illustrates an embodiment of aproximal anchor 700 in which the proximal anchor 700 can be radiallyexpanded such that the relationship between the anchor 700 and theadjacent vertebrae can be adjusted by the surgeon. In this embodiment,the anchor 700 comprises a wall 702, which can be formed of an elasticmaterial. The wall is coupled to an inner member 704 that comprises atubular housing 706 and a proximal flange 708, which can be arranged asdescribed above with reference to FIG. 10B. The wall 702 and the innermember 704 define a cavity 710, which can be filled with an inflationmaterial 712, such as, for example, a gas, liquid, gel, and/orhardenable or semi-hardenable media (e.g., an polymer, epoxy or cement).One or more valves 714 (e.g., a duck bill valve) can be provided alongthe wall 702. An inflation lumen 716 can extend through the valve suchthat the cavity 710 can be inflated with the inflation material 712.After inflation, the lumen 716 is removed and the valve 714 seals thecavity 710. One or more dividing walls 718 can be provided with thecavity 710 such that the anchor 50 can be inflated in discrete orsemi-discrete sections.

In one embodiment of use, the body 28 and proximal anchor 700 areinserted into position as described herein. The cavity 710 is theninflated to expand the proximal anchor 50 and increases its diameter. Inthis manner, the surgeon can control the degree to which the proximalanchor 50 limits the motion of the spine. For example, in oneembodiment, increasing the diameter of the proximal anchor 50 wouldincrease the distance between the two vertebrae. In some embodiments,the inflation material 712 can also be removed such that the dimensionscan be decreased during the same procedure in which the device 12 isinserted into the spine. In still other embodiments, the inflationmaterial 712 can be added or removed in a subsequent, preferably,minimally invasive second procedure such that the degree which theproximal anchor 50 limits the motion of the spine can be adjusted in thesecond, subsequent procedure. In one embodiment, this is done byinserting a lumen through the valve and adding and/or removing theinflation media 712.

FIGS. 20A-D illustrates another embodiment of a proximal anchor 750 inwhich one or more dimensions of the anchor 750 can be adjusted. In thisembodiment, the dimensions are adjusted using a mechanical mechanism.With reference to the illustrated embodiments, the anchor 750 caninclude a proximal member 752 and a distal member 754, which can bemoveably carried by the body 28 as described below. The proximal member752 defines a proximal stop 756 and the distal member 754 defines adistal stop 758. An expandable member 760 is positioned between theproximal and distal stops 756, 758. The expandable member 760 isconfigured to expand radially as the proximal and distal stops 756, 758are moved towards each other and the expandable member 760 is compressedtherebetween. In one embodiment, the expandable member 760 comprises anelastic material that when compressed expands as shown in FIGS. 20A and20B. In another embodiment, the expandable member 760 comprises amalleable material (e.g., a metal or metal alloy) that is provided withone or more slots. In such an embodiment, the slots allow the member 760to expand as it is compressed between the proximal and distal stops 756,758.

With reference to FIG. 20D, the proximal member 752 can be provided witha recess 55 and ring 51 as described above with reference to FIGS. 5 and6. In this manner, the proximal member 752 can be advanced in the distaldirection while proximal movement of the member 752 is resisted. Ofcourse, other complementary retention structures can be used between themember 752 and the body 28 as described to permit distal movement whileresisting proximal movement. The distal movement of the distal member754 can be prevented by a distal stop 762 provided on the body 28. Asshown in FIG. 20D, the distal member 754 can be provided with a smoothbore 764 such that it can be advanced over the body 28 towards thedistal stop 762.

FIG. 21 illustrates an embodiment of a proximal anchor 770 which issimilar to the previous embodiment. In this embodiment, the proximalmember 752 includes threads 772 such that the proximal member 752 can bedistally advanced or proximal retracted by rotation. FIG. 22 illustratesanother embodiment of a proximal anchor 780. In this embodiment, theproximal member 752 is configured as described with reference FIG. 20D.However, the distal member 754 is provided with threads 782 such thatthe position of the distal member 754 on the body 28 can be adjusted.

The above described devices and techniques limit motion of the spine byproviding an abutment or wedge surface on one vertebrae or bodystructure. The abutment surface contacts, abuts, and/or wedges against aportion of a second, adjacent vertebrae or body structure so as limit toat least one degree of motion/freedom between the two vertebra or bodystructure while permitting at least one other degree of motion. Whilethe above described devices and techniques are generally preferred,certain features and aspects can be extended to modified embodiments forlimiting motion between vertebrae. These modified embodiments will nowbe described.

In one embodiment, the proximal anchor 50 of the fixation device may be,coupled to, attached or integrally formed with the body 28. In thismanner, movement between the proximal anchor 50 and the body 28 is notpermitted. Instead, the clinician may chose a fixation device of theproper length and advance the device into the vertebrae until theproximal anchor lies flush with the vertebrae or is otherwise positionedaccordingly with respect to the vertebrae. In one particular,embodiment, the proximal anchor that is coupled to, attached orintegrally formed with the body 28 is configured to have an outersurface which can rotate, preferably freely, with respect to the body28. This arrangement advantageously reduces the tendency of the deviceto rotate and/or move within the inferior vertebrae as the proximalanchor 50 contacts the superior vertebrae.

In another embodiment, the abutment surface may be attached to thevertebrae through the use of an adhesive, fasteners, staples, screws andthe like. In still another embodiment, the abutment surface may formedon a distal end of a stabilization device that is inserted through thefront side of the vertebrae.

In the embodiments described above, the device 12 is generally insertedinto the spine from a posterior position such that a distal end of thedevice 12 is inserted into the first, inferior vertebrae and a proximalend of the device 12 contacts or wedges against the second, superiorvertebrae. However, it is anticipated that certain features and aspectsof the embodiments described herein can be applied to a procedure inwhich the device is inserted from a lateral or anterior site. In such anembodiment, the distal end or side portion of the device may contact orwedge against the second superior vertebrae. Such embodiments provide acontact or wedge surface which is supported by one body structure tolimit of the motion of an adjacent body structure.

In the embodiments, described above, it is generally advantageous thatthe proximal anchor be radiopaque or otherwise configured such that incan be seen with visual aids used during surgery. In this manner, thesurgeon can more accurately position the proximal anchor with respect tothe superior and inferior vertebra.

Preferably, the clinician will have access to an array of fixationdevices 12, having, for example, different diameters, axial lengths and,if applicable, angular relationships. These may be packaged one or moreper package in sterile or non-sterile envelopes or peelable pouches, orin dispensing cartridges which may each hold a plurality of devices 12.The clinician will assess the dimensions and load requirements, andselect a fixation device from the array, which meets the desiredspecifications.

The fixation devices may also be made from conventional non-absorbable,biocompatible materials including stainless steel, titanium, alloysthereof, polymers, composites and the like and equivalents thereof. Inone embodiment, the distal anchor comprises a metal helix, while thebody and the proximal anchor comprise a bioabsorbable material. Inanother embodiment, the body is made of PEEK™ polymer or similar plasticmaterial. Alternatively, the distal anchor comprises a bioabsorbablematerial, and the body and proximal anchor comprise either abioabsorbable material or a non-absorbable material. As a furtheralternative, each of the distal anchor and the body comprise anon-absorbable material, connected by an absorbable link. This may beaccomplished by providing a concentric fit between the distal anchor andthe body, with a transverse absorbable pin extending therethrough. Thisembodiment will enable removal of the body following dissipation of thepin, while leaving the distal anchor within the bone.

The components of embodiments of the present inventions may besterilized by any of the well known sterilization techniques, dependingon the type of material. Suitable sterilization techniques include, butnot limited to heat sterilization, radiation sterilization, such ascobalt 60 irradiation or electron beams, ethylene oxide sterilization,and the like.

The specific dimensions of any of the embodiments of the bone fixationdevices of the present inventions can be readily varied depending uponthe intended application, as will be apparent to those of skill in theart in view of the disclosure herein. Moreover, although the presentinventions have been described in terms of certain preferredembodiments, other embodiments of the inventions including variations indimensions, configuration and materials will be apparent to those ofskill in the art in view of the disclosure herein. In addition, allfeatures discussed in connection with any one embodiment herein can bereadily adapted for use in other embodiments herein. The use ofdifferent terms or reference numerals for similar features in differentembodiments does not imply differences other than those which may beexpressly set forth. Accordingly, the present inventions are intended tobe described solely by reference to the appended claims, and not limitedto the embodiments disclosed herein.

As mentioned above, the dynamic stabilization device 12 can provideadjacent level support as an adjunct to fusion therapy. In oneembodiment, the fusion therapy involves the fixation device 800, whichwill be described in detail below. The fixation device 800 can bepositioned below (or above in other embodiments) the stabilizationdevice 12 and can be used to promote spinal fusion below the spinallevel at which motion is limited by the dynamic stabilization device.

FIGS. 23A-D illustrate an embodiment of the bone fixation device 800having a body 802 and a proximal anchor 804. In this embodiment, thebody 802 comprises a first portion 806 and a second portion 808 that arecoupled together at a junction 810 (FIG. 23D). In the illustratedembodiment, the first portion 806 carries a distal anchor 812 while thesecond portion 808 forms a proximal end 814 of the body 802. The firstand second portions 806, 808 are preferably detachably coupled to eachother at the junction 810. In the illustrated embodiment, the first andsecond portions 806, 808 are detachably coupled to each other viainterlocking threads. Specifically, as best seen in FIG. 23D, the body802 includes an inner surface 816, which defines a central lumen 818that preferably extends from the proximal end 814 to a distal end 820throughout the body 802. At the proximal end of the first portion 806,the inner surface 816 includes a first threaded portion 822. The firstthreaded portion 822 is configured to mate with a second threadedportion 824, which is located on the outer surface 826 of the secondportion 808. The interlocking annular threads of the first and secondthreaded portions 822, 824 allow the first and second portions 806, 808to be detachably coupled to each other. In one modified embodiment, theorientation of the first and second threaded portions 822, 824 can bereversed. That is, the first threaded portion 822 can be located on theouter surface of the first portion 806 and the second threaded portion824 can be located on the inner surface 816 at the distal end of thesecond portion 808. Any of a variety of other releasable complementaryengagement structures may also be used, to allow removal of secondportion 808 following implantation, as is discussed below.

In a modified arrangement, the second portion 808 can comprise any of avariety of tensioning elements for permitting proximal tension to beplaced on the distal anchor 812 while the proximal anchor 804 isadvanced distally. For example, any of a variety of tubes or wires canbe removably attached to the first portion 806 and extend proximally tothe proximal handpiece. In one such arrangement, the first portion 806can include a releasable connector in the form of a latching element,such as an eye or hook. The second portion 808 can include acomplementary releasable connector (e.g., a complementary hook or eye)for engaging the first portion 806. In this manner, the second portion808 can be detachably coupled to the first portion 806 such thatproximal traction can be applied to the first portion 806 through thesecond portion 808 as will be explained below. Alternatively, the secondportion 808 may be provided with an eye or hook, or transverse bar,around which or through which a suture or wire may be advanced, bothends of which are retained at the proximal end of the device. Followingproximal tension on the tensioning element during the compression step,one end of the suture or wire is released, and the other end may bepulled free of the device. Alternate releasable proximal tensioningstructures may be devised by those of skill in the art in view of thedisclosure herein.

With particular reference to FIGS. 23A-23D, the proximal end 814 of thebody 802 may be provided with a rotational coupling 828, for allowingthe second portion 808 of the body 802 to be rotationally coupled to arotation device. The proximal end 814 of the body 808 may be desirablyrotated to accomplish one or two discrete functions. In one applicationof embodiments of the present inventions, the proximal end 814 isrotated to remove the second portion 808 of the body 802 followingtensioning of the device to anchor an attachment to the bone. Rotationof the rotational coupling 828 may also be utilized to rotationallydrive the distal anchor into the bone. Any of a variety of rotationdevices may be utilized, such as electric drills or hand tools, whichallow the clinician to manually rotate the proximal end 814 of the body802. Thus, the rotational coupling 828 may have any of a variety ofcross sectional configurations, such as one or more flats or splines.

With particular reference to FIG. 23A, the fixation device may includean antirotation lock between the first portion 806 of the body 802 andthe proximal anchor 804. In the illustrated embodiment, the firstportion 806 includes a pair of flat sides 830, which interact withcorresponding flat structures 832 in the proximal anchor 804. One orthree or more axially extending flats may also be used. As such,rotation of the proximal anchor 804 is transmitted to the first portion806 and the distal anchor 812 of the body 802. Of course, those of skillin the art will recognize various other types of splines or otherinterfit structures can be used to prevent relative rotation of theproximal anchor and the first portion 806 of the body 802. For example,in one embodiment, the first portion 806 may include three flat sides,which interact with corresponding flat structures on the proximal anchor804.

To rotate the proximal anchor 804, a flange 834 is preferably providedwith a gripping structure to permit an insertion tool to rotate theflange 834. Any of a variety of gripping structures may be provided,such as one or more slots, flats, bores or the like. In one embodiment,the flange 834 is provided with a polygonal, and, in particular, apentagonal or hexagonal recess 836. See FIG. 24A.

In FIGS. 23B and 23C, the proximal anchor 804 is shown in combinationwith a washer 840 that can be configured to interact with a head of theproximal anchor. The washer 840 can include a base and a side wall. Thebase and side wall can define a curved, semi-spherical or radiusedsurface that interacts with the corresponding curved, semi-spherical orradiused surface of the head. The surface surrounds an aperture formedin the base. This arrangement can allow the housing and/or body toextend through and pivot with respect to the washer. A detaileddescription of the washer 840 can be found in U.S. Pat. No. 6,951,561issued on Oct. 4, 2005 entitled “PROXIMAL ANCHORS FOR BONE FIXATIONSYSTEM,” the entirety of the contents of which are incorporated hereinby reference.

FIGS. 24A-F illustrate in more detail the proximal anchor 804 of FIGS.23A-C. This embodiment can include a tubular housing 842. A detaileddescription of the tubular housing 842 can be found in U.S. Pat. No.6,951,561 referred to above. In the illustrated embodiment, the tubularhousing 842 can be attached to, coupled to, or integrally formed(partially or wholly) with a secondary tubular housing 844, whichincludes one or more anti-rotational features 846 (e.g., flat sides) forengaging corresponding anti-rotational features formed on the pin, whichcan be similar to the first portion 806 (e.g., see description above).The flange or collar 834 is attached, coupled or integrally formed withthe proximal end of the secondary tubular housing. Teeth or flanges 848on bridges 850 may also be configured such that the proximal anchor maybe distally advanced and/or removed with rotation. The illustratedembodiment also advantageously includes visual indicia 852 (e.g., marks,grooves, ridges etc.) on the tubular housing 842 for indicating thedepth of the proximal anchor 804 within the bone.

In one embodiment of use, the fixation device 800 of FIGS. 23A-C canhave an axial length and outside diameter suitable for a hole drilled inthe bone. The distal end 820 of the fixation device 800 is advanceddistally into the hole until the distal anchor 812 reaches the distalend of the hole. The proximal anchor 804 may be carried by the fixationdevice 800 prior to advancing the body 802 into the hole, or may beattached following placement of the body 802 within the hole. Once thebody 802 and proximal anchor 804 are in place, the clinician may use anyof a variety of driving devices, such as electric drills or hand toolsto rotate the proximal anchor 804 and thus cancellous bone anchor 812into the head of the femur. In modified embodiments, the fixation deviceis configured to be self-drilling or self tapping such that a hole doesnot have to be formed before insertion into the bone.

Once the anchor 812 is in the desired location, proximal traction isapplied to the proximal end 814 of body 802, such as by conventionalhemostats, pliers or a calibrated loading device, while distal force isapplied to the proximal anchor 804. In this manner, the proximal anchor804 is advanced distally until the anchor 804 fits snugly against theouter surface of the bone. Appropriate tensioning of the fixation device800 is accomplished by tactile feedback or through the use of acalibration device for applying a predetermined load on the implantationdevice. One advantage of the structure of certain embodiments is theability to adjust compression independently of the setting of the distalanchor 812.

Following appropriate tensioning of the proximal anchor 804, the secondportion 808 of the body 802 is preferably detached from the firstportion 806 and removed. In the illustrated embodiment, this involvesrotating the second portion 808 with respect to the first portion viathe coupling 828. Following removal of the second portion 808 of eachbody 802, the access site may be closed and dressed in accordance withconventional wound closure techniques.

An advantage of certain embodiments of the fixation devices disclosedabove is that the proximal anchor provides the device with a workingrange such that one device may accommodate varying distances between thedistal anchor and the proximal anchor. In certain applications, thisallows the technician to focus on the proper positioning of the distalanchor with the knowledge that the proximal anchor lies within theworking range of the device. With the distal anchor positioned at thedesired location, the proximal anchor may then be advanced along thebody to compress the fracture and/or provide stability between bones. Ina similar manner, the working range provides the technician withflexibility to adjust the depth of the proximal anchor. For example, insome circumstances, the bone may include voids, cysts, osteoporotic bonethat impairs the stability of the distal anchor in the bone.Accordingly, in some circumstances, the technician may advance thedistal anchor and then desire to retract the distal anchor such that itis better positioned in the bone. In another circumstance, thetechnician may inadvertently advance the distal tip through the boneinto a joint space or other undesired area (e.g., spinal canal). In suchcircumstances, the working range of the device allows the technician toreverse and retract the anchor and recompress. Such adjustments arefacilitated by the working range of the proximal anchor on the body.

Preferably, the clinician will have access to an array of fixationdevices (e.g., fixation device 800) having, for example, differentdiameters, axial lengths and angular relationships. These may bepackaged one per package in sterile envelopes or peelable pouches, or indispensing cartridges which may each hold a plurality of devices 800.Upon encountering a use for which the use of a fixation device is deemedappropriate, the clinician will assess the dimensions and loadrequirements, and select a fixation device from the array which meetsthe desired specifications.

The fixation devices described above may be used in any of a widevariety of anatomical settings beside the spine as has been discussed.For example, lateral and medial malleolar fractures can be readily fixedusing the device according to certain embodiments. For example, thefixation devices 800 can be used with the distal fibula and tibia. Thefibula terminates distally in the lateral malleolus, and the tibiaterminates distally in the medial malleolus. A fixation device 800 canextend through the lateral malleolus across the lateral malleolarfracture and into the fibula. The fixation device 800 can include adistal anchor for fixation within the fibula, an elongate body and aproximal anchor as has been discussed.

As mentioned above, the devices describe herein may also be used forspinal fixation. In embodiments optimized for spinal fixation in anadult human population, the body 800 can generally be within the rangeof from about 20-90 mm in length and within the range of from about3.0-8.5 mm in maximum diameter. The length of the helical anchor,discussed above, may be about 8-80 millimeters. Of course, it isunderstood that these dimensions are illustrative and that they may bevaried as required for a particular patient or procedure.

In spinal fixation applications, the fixation device 800 may be used asa trans-facet screw. That is, the fixation device extends through afacet of a first vertebra and into the facet of a second, typicallyinferior, vertebra, which vertebrae are referred to above asintermediate and inferior vertebral bodies. This procedure is typically(but not necessarily) performed with bilateral symmetry. Thus, even inthe absence of a stabilizing bar tying pedicle screws to adjacentvertebrae or to the sacrum, and in the absence of translaminar screwsthat can extend through the spinous process, the fixation devices can beused to stabilize two vertebrae, such as L3 and L4 to each other pendingthe healing of a fusion. In one embodiment, the body 802 of fixationdevice 800 can have a length of approximately 10 mm-30 mm and thediameter of the body 802 can be approximately 3 mm to 5.5 mm.

The fixation device 800 may also be used as a trans-laminar facet screw.In this embodiment of use, the fixation device extends through thespinous process and facet of a first vertebra and into the facet of asecond, typically inferior, vertebra. As with the previous embodiment,this procedure is typically (but not necessarily) performed withbilateral symmetry. In one embodiment, the body 802 of fixation device800 can have a length of approximately 50 mm-90 mm and the diameter ofthe body is approximately 4 mm to 5.5 mm.

The fixation device may also be used is used as a facet-pedical screw(e.g., as used in the Boucher technique). In such an embodiment, thefixation device extends through the facet of a first vertebra and intothe pedicle a second, typically inferior, vertebra. As with the previousembodiment, this procedure is typically (but not necessarily) performedwith bilateral symmetry. In such an embodiment, the fixation device 800and the body 802 can be approximately 20-40 millimeters in length and3.0-5.5 millimeters in diameter.

FIGS. 25A-D illustrate another embodiment of a proximal anchor 860. Inthis embodiment, the proximal anchor 860 includes a recess 862configured to receive a split ring 864. As will be explained in detailbelow, the proximal anchor 860 can include an anti-rotation feature tolimit or prevent rotation of the ring 864 within the proximal anchor860. In light of the disclosure herein, those of skill in the art willrecognize various different configurations for limiting the rotation ofthe ring 864. However, a particularly advantageous arrangement will bedescribed below with reference to the illustrated embodiment.

In the illustrated embodiment, the proximal anchor 860 has a tubularhousing 868 that can engage with a body 802 or a first portion 806 ofthe body 802, as described above. With reference to FIGS. 25B and 25D,the tubular housing 868 comprises one or more anti-rotational features870 in the form of a plurality of flat sides that are configured to matecorresponding anti-rotational features 872 or flat sides of the body 802of the fixation device 800. As shown in FIG. 25D, in the illustratedembodiment, the body 802 has three flat sides 872. Disposed between theflat sides 872 are the portions of the body 802 which include thecomplementary locking structures such as threads or ratchet likestructures as described above. The complementary locking structuresinteract with the ring 864 as described above to resist proximalmovement of the anchor 860 under normal use conditions while permittingdistal movement of the anchor 860 over the body 802.

As mentioned above, the ring 864 is positioned within the recess 862. Inthe illustrated embodiment, the recess 862 and ring 864 are positionednear to and proximal of the anti-rotational features 870. However, thering 864 can be located at any suitable position along the tubularhousing 868 such that the ring 864 can interact with the retentionfeatures of the body 802.

During operation, the ring 864 may rotate to a position such that thegap 874 between the ends 876, 878 of the ring 864 lies above thecomplementary retention structures on the body 802. When the ring 865 isin this position, there is a reduced contact area between the split ring864 the complementary retention structures thereby reducing the lockingstrength between the proximal anchor 860 and the body 802. In theillustrated embodiment, for example, the locking strength may be reducedby about ⅓ when the gap 874 over the complementary retention structuresbetween flat sides 872. As such, it is advantageous to position the gap874 on the flat sides 872 of the body 802 that do not includecomplementary retention structures.

To achieve this goal, the illustrated embodiment includes a pair of tabs880, 882 that extend radially inward from the interior of the proximalanchor 800. The tabs 880, 882 are configured to limit or preventrotational movement of the ring 864 relative to the housing 804 of theanchor 800. In this manner, the gap 874 of the ring 864 may bepositioned over the flattened sides 872 of the body 802.

In the illustrated embodiment, the tabs 880, 882 have a generallyrectangular shape and have a generally uniform thickness. However, it iscontemplated that the tabs 880, 882 can be square, curved, or any othersuitable shape for engaging with the ring 864 as described herein.

In the illustrated embodiment, the tabs 880, 882 are formed by making anH-shaped cut 884 in the tubular housing 860 and bending the tabs 880,882 inwardly as shown in FIG. 25D. As shown in FIG. 25D, the tabs 880,882 (illustrated in phantom) are interposed between the edges 876, 878of the ring 864. The edges 876, 878 of the ring 864 can contact the tabsto limit the rotational movement of the ring 864. Those skilled in theart will recognize that there are many suitable manners for forming thetabs 880, 882. In addition, in other embodiments, the tabs 880, 882 maybe replaced by a one or more elements or protrusions attached to orformed on the interior of the proximal anchor 860.

For the embodiments discussed herein, the pin, together with the distalanchor, and other components, can be manufactured in accordance with anyof a variety of techniques which are well known in the art, using any ofa variety of medical-grade construction materials. For example, the pinbody and other components can be injection-molded from a variety ofmedical-grade polymers including high or other density polyethylene,nylon and polypropylene. The distal anchor can be separately formed fromthe pin body and secured thereto in a post-molding operation, using anyof a variety of securing techniques such as solvent bonding, thermalbonding, adhesives, interference fits, pivotable pin and aperturerelationships, and others known in the art. Preferably, however, thedistal anchor is integrally molded with the pin body, if the desiredmaterial has appropriate physical properties.

Retention structures can also be integrally molded with the pin body.Alternatively, retention structures can be machined or pressed into thepin body in a post-molding operation, or secured using other techniquesdepending upon the particular design. Further, as recited in U.S. Pat.No. 6,951,561 referred to above, a variety of polymers, such asbioabsorbable polymers, can be used to fabricate components of theembodiments disclosed herein.

As shown in FIG. 26, the fixation devices 800 a, 800 b may be used toprovide stability without additional hardware. In this example, thefixation devices 800 a, 800 b is used similarly to a trans-facet screw.That is, the fixation devices 800 a, 800 b extend through a facet of afirst vertebra and into the facet of a second, typically inferior,vertebrae. As in the illustrated embodiment, this procedure is typically(but not necessarily) performed with bilateral symmetry. Thus, even inthe absence of a stabilizing bar tying pedicle screws to adjacentvertebrae or to the sacrum, and in the absence of translaminar screwsthat can extend through the spinous process, the fixation devices 800 a,800 b can be used to stabilize two vertebrae, such as L3 and L4 to eachother pending the healing of a fusion. In one embodiment, the body offixation devices 800 a, 800 b can have a length of approximately 10mm-30 mm and the diameter of the body is approximately 3 mm to 5.5 mm.

In the embodiment of FIG. 26, the flange of the proximal anchor istypically supported directly against the outer surface of a vertebra.Because the outer surface is typically non-planar and/or the insertionangle of the fixation device is not perpendicular to the outer surface,an angularly fixed flange may contact only a portion of the outersurface. That is, the contact surface of the flange may not sit flush onthe outer surface of the vertebra. This may cause the vertebra to crackdue to high stress concentrations. This can result in poor fusion rates.

As such, in these applications, angularly adjustable flanges can beparticularly advantageous because the flange can rotate with respect tothe body and thereby the bone contacting surface may be positioned moreclosely to the outer surface of the vertebra. This can result in morebone contacting surface being utilized and the stress supported by thefixation device is spread out over a larger area of the vertebra. Theseangularly adjustable flanges may also be used with the spinal cages androds. In such embodiments, the angle of the body fixation device may benot be perpendicular to the contact surface of the fixation rod orplate. In such situations, the angularly adjustable flange allows theflange to rotate and sit flush against the fixation rod and plate.

In the above embodiments, it may be advantageous to drill a counter boreinto the first vertebra for receiving a portion of the proximal anchor.In such embodiments, the counter bore will typically have a diameterthat is slightly larger than the outer diameter of the proximal anchorso that the proximal anchor may sit at least partially below the outersurface of the vertebra.

In certain regions of the spine, the dimension transverse to a facetjoint and through the adjacent facets is relatively small. In thesecircumstances, the fixation may desirably include a through bore,opening through the distal cortex of the distal facet. The fixationdevice described above may be utilized either in a blind holeapplication, which the distal anchor is buried within the bone, or athrough bore application is which the distal helix extends into andpotentially through the distal cortex. However, a through bore fixationdevice may also be used.

The fixation devices 800 are preferably installed using a percutaneousor minimally invasive approach in which the procedure is done throughone or more percutaneous small openings in a manner similar to thatdescribed above with respect to the stabilization devices 12. Asmentioned above, the fixation device 800 can be positioned below (orabove in other embodiments) the stabilization device 12, which can beused to promote spinal fusion below the spinal level at which motion islimited by the dynamic stabilization device 12. In such an embodiment,the dynamic stabilization device can provide adjacent level support asan adjunct to fusion therapy. An advantage of this system and techniqueis that both the stabilization device 12 and the fixation device 800 canbe inserted into the spine utilizing a minimally invasive approach inwhich the procedure is done through one or more percutaneous smallopenings. In other embodiments, the fixation devices 800 can be replacedand/or supplemented with other fixation devices of the type known in theart such as, for example, pedicle screws and rod constructs, cages, etc.

FIGS. 27-28 are rear and side elevational views of the cervical spine inaccordance with another embodiment. The methods and devices disclosedherein can be used in various areas along the spinal column and can becombined with other methods and devices. For example, FIGS. 27-28illustrate that at least one of the dynamic stabilization device 12 andthe fixation device 800 can be used in the cervical vertebrae area ofthe spine. As shown however, the dynamic stabilization device 12 isillustrated. In embodiments wherein the dynamic stabilization device 12is used in the cervical spine, for example, it is contemplated that theconfiguration of the dynamic stabilization device 12 has a length fromabout 5 mm to about 25 mm when configured for the cervical spine. Thedynamic stabilization device 12 can therefore be specifically configuredfor uses in various parts of the spine.

In addition, the components disclosed herein may be provided with any ofa variety of structural modifications to accomplish various objectives,such as osteoincorporation, or more rapid or uniform absorption into thebody. For example, osteoincorporation may be enhanced by providing amicropitted or otherwise textured surface on the components.Alternatively, capillary pathways may be provided throughout the pin andcollar, such as by manufacturing the components from an open cell foammaterial, which produces tortuous pathways through the device. Thisconstruction increases the surface area of the device which is exposedto body fluids, thereby generally increasing the absorption rate.Capillary pathways may alternatively be provided by laser drilling orother technique, which will be understood by those of skill in the artin view of the disclosure herein. In general, the extent to which thecomponent can be permeated by capillary pathways or open cell foampassageways may be determined by balancing the desired structuralintegrity of the device with the desired reabsorption time, taking intoaccount the particular strength and absorption characteristics of thedesired polymer.

The component of the embodiments disclosed herein may be sterilized byany of the well known sterilization techniques, depending on the type ofmaterial. Suitable sterilization techniques include heat sterilization,radiation sterilization, such as cobalt 60 irradiation or electronbeams, ethylene oxide sterilization, and the like.

The specific dimensions of any of the components and bone fixationdevices can be readily varied depending upon the intended application,as will be apparent to those of skill in the art in view of thedisclosure herein. Moreover, the components and devices have beendescribed in terms of certain preferred embodiments, other embodimentsincluding variations in the number of parts, dimensions, configurationand materials will be apparent to those of skill in the art in view ofthe disclosure herein. In addition, all features discussed in connectionwith any one embodiment herein can be readily adapted for use in otherembodiments herein to form various combinations and sub-combinations.The use of different terms or reference numerals for similar features indifferent embodiments does not imply differences other than those whichmay be expressly set forth. Accordingly, the present inventions areintended to be described solely by reference to the appended claims, andnot limited to the preferred embodiments disclosed herein.

1. A method of limiting at least one degree of movement between asuperior vertebral body, an intermediate vertebral body, and an inferiorvertebral body of a patient, the intermediate vertebral body beingdisposed between the superior and inferior vertebral bodies entirelyfrom posterior access sites, comprising: advancing a distal end of astabilization device into an intermediate vertebral body from aposterior access site; positioning, from a posterior access site, aproximal portion of the stabilization device such that the proximalportion limits movement between the superior vertebral body and theintermediate vertebral body while providing at least some degree betweenthe superior vertebral body and the intermediate vertebral body; andadvancing, from a posterior access site, a distal end of a fixationdevice into the intermediate vertebral body and into the inferiorvertebral body for stabilizing the intermediate vertebral body and theinferior vertebral body to allow fusion between the intermediatevertebral body and the inferior vertebral body.
 2. The method of claim1, further comprising maintaining the patient in a face down positionduring the step of advancing a distal end of a stabilization device intothe intermediate vertebral body.
 3. The method of claim 1, wherein thesteps of advancing a distal end of a stabilization device into a pedicleof the intermediate vertebral body and positioning a proximal portion ofthe stabilization device are accomplished through a minimally invasivesurgical approach.
 4. The method of claim 1, wherein advancing a distalend of a stabilization device the intermediate vertebral body furthercomprises advancing the stabilization device over a guidewire.
 5. Themethod of claim 1, wherein advancing a distal end of a stabilizationdevice into the intermediate vertebral body further comprises advancingthe stabilization device through an expanded tissue tract
 6. The methodof claim 1, wherein the superior vertebral is located caudal to theinferior superior body.